Syrian forces shelled rebels in the battle-scarred city of Aleppo Sunday and gunfire was heard in Damascus, as US Secretary of State Hillary Clinton called for the regime's downfall to be speeded up.
The Shaar, Tariq al-Bab, Sakhur, Hanano and Bustan al-Qasr neighbourhoods all came under bombardment, as troops pressed a ground offensive they launched on Wednesday the Syrian Observatory for Human Rights said.
An army colonel was killed in an assault by rebels in the Safira district, the Britain-based watchdog said.
In the capital Damascus, gunfire was reported in the Qadam neighbourhood.
Heavy explosions were heard in the Damascus suburb of Harasta, the Observatory said. Elsewhere in the province, machinegun fire was heard in the town of Al-Tal, where 15 civilians were killed in shelling and clashes on Saturday as troops tried to regain control from rebels.
They were among 148 people killed across Syria on Saturday -- 85 civilians, 20 rebels and 43 soldiers, the Observatory said.
A rebel commander insisted his fighters were still putting up strong resistance around Salaheddin.
"Fierce fighting has continued without respite for the past 24 hours as the army tries to push us out of the neighbourhood," Abdel Qader Saleh told AFP by telephone.
The Local Coordination Committees, a network of activists on the ground, reported "intense and indiscriminate bombardment by aircraft flying over Sakhur and Hanano districts" of Aleppo, Syria's commercial capital.
Troops backed by artillery stormed Salaheddin on Wednesday in the first stage of an offensive to recapture areas of the northern city taken by the rebels since July 20.
In the face of the escalating violence, Clinton said in Turkey the "number one goal" of Washington and Ankara was to hasten the end of President Bashar al-Assad's regime and stop the bloodshed.
"We are continuing to increase pressure from outside," she told reporters in Istanbul after meeting Turkish Foreign Minister Ahmet Davutoglu and Syrian opposition activists.
"Yesterday in Washington we announced sanctions designed to expose and disrupt the links between Iran, Hezbollah and Syria that prolong the life of the Assad regime."
Washington on Friday announced sanctions against Syrian state oil company Sytrol for trading with Iran, in a bid to starve both Tehran and Damascus of much-needed revenue.
The US Treasury also said it was adding the Iran- and Syria-backed Lebanese Shiite militant group Hezbollah to a blacklist of organisations targeted under Syria-related sanctions.
The move explicitly ties the group to the violence in Syria, where Assad is attempting to put down a 17-month revolt that has reportedly killed more than 21,000 people.
But the violence raged on with blasts in Damascus Saturday that triggered panic among residents.
Official SANA news agency said "armed terrorists" blew up a bomb in Marje district and later "opened fire indiscriminately to terrorise civilians."
But a militant said "fighters of the (rebel) Free Syrian Army fired an RPG on a security convoy near Victoria Bridge" and later exchanged fire with government forces.
Videos uploaded by activists on the Internet showed panicked residents running in the streets and others blowing the horns of their cars to force traffic to move.
Fighting was also reported in Tadamun, another Damascus area, where there were "fierce clashes between the Free Syrian Army and the regime forces," said the Local Coordination Committees.
With the unrelenting violence, Arab foreign ministers are to hold emergency talks in Saudi Arabia on Sunday to discuss the conflict and a replacement for international mediator Kofi Annan, who quit in frustration over a failed peace plan.
World powers are expected to name veteran Algerian diplomat Lakhdar Brahimi as the new UN-Arab League envoy for Syria early next week.
UN Secretary General Ban Ki-moon is pushing for a UN presence in Syria after its observer mission in the country expires on August 19 and has suggested options for an "effective and flexible presence," a diplomat said in New York on Saturday.
The mission was deployed in April to oversee a peace plan, which should have begun with a ceasefire that never took hold and in mid-June, the observers suspended patrols as fighting intensified.
The Security Council is to debate the future of the mission on Thursday.
On the humanitarian front, the United States, Canada pledged new funds for Syrian refugees who fled the violence in their country while France sent a cargo plane to Jordan with tonnes of aid for those forced to flee.
Clinton announced an additional $5.5 million in aid while in Turkey, while Canadian Foreign Minister John Baird said his country was providing Jordan with $6.5 million to meet the needs of the refugees.
Turkey is currently home to some 55,000 refugees living in camps along the Syrian border and Jordan is hosting more than 150,000 Syrians.
In Lebanon, another neighbour where tensions have spilled over, the military prosecutor general accused Syrian security chief General Ali Mamluk and former Lebanese minister Michel Samaha of planning attacks.
A judicial source said they were "suspected of forming a group to provoke sectarian killings and terrorist acts using explosives, which were transported and stored by Michel Samaha."