CAIRO — Two Western journalists, one American and one French, were killed early Wednesday as forces loyal to President Bashar al-Assad pursued a deadly bombardment of the central city of Homs, according to activists and officials.

Valérie Pécresse, the French government spokeswoman, identified the dead as Marie Colvin, an American reporter working for The Sunday Times of London, and Rémi Ochlik, a French photographer.

The deaths were reported less than a week after Anthony Shadid, a correspondent for The New York Times, died last Thursday of an apparent asthma attack on his way back to Turkey after spending nearly a week reporting covertly inside Syria.

Video footage posted on social networking sites showed what seemed to be two bodies lying face down in rubble inside a building identified in news reports as a makeshift media center in a beleaguered neighborhood of Homs, where rebels have been under sustained fire for almost three weeks. Three other Western journalists were injured in the attack, activists said.

According to his Web site, Mr. Ochlik, in his late twenties, had covered wars and upheaval in Haiti, Congo and the Middle East. Ms. Colvin, 55, was a veteran of many conflicts from the Middle East to Sri Lanka, where she lost an eye covering a civil war. She wore a distinctive black eyepatch.

Jon Snow, an anchor for Britain’s channel 4 News, which interviewed her from Homs on Tuesday evening, called her “the most courageous journalist I ever knew and a wonderful reporter and writer.”

In an article published on Feb. 19 in The Sunday Times, Ms. Colvin described with how she entered Homs “on a smugglers’ route, which I promised not to reveal, climbing over walls in the dark and slipping into muddy trenches. Arriving in the darkened city in the early hours, I was met by a welcoming party keen for foreign journalists to reveal the city’s plight to the world. So desperate were they that they bundled me into an open truck and drove at speed with the headlights on, everyone standing in the back shouting Allahu akbar" — God is the greatest. Inevitably, the Syrian army opened fire.”

“When everyone had calmed down I was driven in a small car, its lights off, along dark empty streets, the danger palpable. As we passed an open stretch of road, a Syrian army unit fired on the car again with machine guns and launched a rocket-propelled grenade,” Ms. Colvin wrote.

“The scale of human tragedy in the city is immense. The inhabitants are living in terror. Almost every family seems to have suffered the death or injury of a loved one,” she wrote.

Quoting a witness reached from neighboring Jordan, Reuters said the two journalists died when shells hit the house in which they were staying and a rocket hit them when they were escaping.

An activist who spoke in return for anonymity for fear of government reprisals said an apartment being used as a media center with satellite uplink facilities had taken a direct hit and activists had been unable to reach it to retrieve the bodies because of continued shelling.

The killings were reported as intense international lobbying for and against Mr. Assad continued on Tuesday over the nearly yearlong crackdown that has proved the most violent of the so-called Arab Spring and one of the most perilous for journalists trying to cover it.

The Syrian authorities do not routinely grant visas for reporters to enter the country and seek to control those who are given rare permission to do so. Unlike other violent uprisings in Libya or Yemen, those controls have combined to make the Syrian revolt difficult to observe first-hand and those reporters that do so run great risks of being caught in fighting, often in isolated pockets of rebel resistance.

Previous fatalities include a freelance cameraman, Ferzat Jarban, who was found dead in early November. Another freelance cameraman, Basil al-Sayed, died at the end of December. A French television reporter, Gilles Jacquier, died in January during a government-sponsored trip to Homs. Mazhar Tayyara, a freelance reporter for Agence France-Presse, The Guardian and other publications, died in Homs in early February.

In addition to reporters from traditional media, the conflict throughout the Arab world has drawn in a generation of citizen journalists using cell phones, blogs and social media sites to spread word of their plight.

The deaths of the Western journalists reported on Wednesday followed by one day the death of Rami el Sayed, a well-known videoblogger in Baba Amr. Other citizen journalists in Homs have been killed recently in what activists interpret as part of a deliberate campaign to choke off news of the opposition.

“It’s too much of a coincidence,” said a Syrian activist in Cairo who has followed events closely. “There are reports of planes flying around and they may be looking for the satellite uplinks.”

Homs has been an epicenter of the fighting in recent weeks, but government assaults were also reported on Tuesday in the Idlib area in the north and elsewhere. The day’s toll, as compiled by various groups that try to track the violence from inside and outside the country, ranged from the dozens upward.

At the same time, the faction of the opposition that is armed has claimed several more lives, according to the Syrian government, whose news agency reported the funerals of three soldiers killed in or near Damascus and in the central city of Hama.

Russia announced that it would not participate in a meeting in Tunisia on Friday of a contact group of Western and Arab nations, Friends of Syria, where opposition figures were expected to lobby for greater international recognition and support. The Syrian government’s news agency, SANA, reported that a Chinese special envoy to the Middle East, Wu Sike, visited Damascus on Tuesday and called for dialogue with all sides in the crisis.

SANA also reported from Beijing on a news conference by the Chinese Foreign Ministry spokesman, Hong Li, in which he called for “the international community to respect the sovereignty, stability and unity of Syria.” He did not say whether China would attend the Friends of Syria conference.

Iranian officials, at a regular Foreign Ministry news conference in Tehran, did not explicitly discuss the conference, but denounced Western meddling in the affairs of Syria, its longstanding ally, as benefiting Israel at the expense of those who resist its power.

“What is happening in Syria serves the best interests of Israel and weakens the resistance,” said a ministry spokesman, Ramin Mehmanparast, as quoted by SANA.

But the United States threw some of the Iranians’ support for Syria into question, suggesting that Iran’s reports that it has sent two warships to help train Syrian forces were false. “We have absolutely no indication whatsoever the Iranian ships ever docked in Syrian ports,” a Pentagon spokesman, George Little, was quoted by Reuters as saying.

Iran’s Press TV satellite broadcaster had said the two ships, a destroyer and a supply ship, docked in Tartus, Syria, on Saturday “to provide maritime training to naval forces of Syria under an agreement signed between Tehran and Damascus a year ago.”

Red Cross officials did not respond to calls on Tuesday seeking to establish whether the organization’s efforts to secure even a brief cease-fire from government forces had been successful. But based on reports from activist groups and official Syrian news media, the violence appeared unabated.

The assault on Homs appeared to be a continuation of a government attack that began Feb. 4, after China and Russia vetoed a United Nations Security Council resolution condemning the violence and backing an Arab League plan for Mr. Assad to step aside. (Last week, in the strongest international rebuke to date, the General Assembly voted overwhelmingly to pass the same resolution in nonbinding form.)

A new group based in Cairo, the Activist News Association, has been collecting information from a network of “citizen journalist” contacts inside of Syria. Rami Jarrah, a Syrian activist who helped create the group, said that Syrian government and ground forces were massing outside of Homs. “Active resistance has long since stopped, but the government is using the excuse of ‘armed resistance,’ in quotes, to continue this bombardment,” Mr. Jarrah said. “They’re killing the democratic movement.”

Based on photographs of victims sent from inside Syria, he said, at least 79 deaths took place around the country on Tuesday, 46 of them in Homs, where shelling of the Sunni Arab neighborhood of Baba Amr was particularly heavy, and 33 in Idlib. That toll was likely to rise, he said.

Another exile activist group, the Syrian Observatory for Human Rights, reported that in the northern city of Aleppo, unknown gunmen shot and killed Mohammad Ramadan, a businessman who supported the government. It also reported scattered protests and skirmishing in the capital, Damascus, where a group of youths raised an opposition flag at the Jaawzeh Bridge at the southern entrance of the capital.

Meanwhile, the Hamas authorities in the Gaza Strip allowed Palestinians to demonstrate against Mr. Assad for the first time, a move that came weeks after the top Hamas leadership abandoned its longtime base in Damascus. The unusual rally was organized by a group called the Palestinian Gathering to Support Syrian People, a new body run by the sons of late Hamas leaders from Gaza.

About 200 students rallied at Islamic University before marching with Palestinian and Syrian flags to downtown Gaza. There, about 100 more Palestinians, including women, joined the rally. The protesters burned posters of Mr. Assad and carried banners bearing slogans like “Allah, Syria and freedom,” and “Shame on child murderers.”

The Hamas leadership has refused to express support for Mr. Assad despite pressure from Iran, a main backer of Hamas. But with about 650,000 Palestinian refugees living in Syria, Hamas officials are unlikely to draw Syrian ire by openly criticizing the leadership.