(CNN) -- A video purportedly released by a shadowy, Syrian-based terrorist group claimed responsibility Saturday for dual suicide bombings that killed dozens and wounded hundreds in the country's capital this week.
The two-minute video, apparently by jihadist group Al Nusra Front, says government buildings were targeted "because the regime continues to shell residential civilians in Damascus countryside, Idlib, Hama, Daraa and other areas. And we remained true to our promise to respond to this shelling with strikes."
Syrian Prime Minister Adel Safar visited the site of the bombings in Damascus on Saturday, state-run media reported.
The suicide attacks were aimed "at striking Syria's will and its people in life, security and stability," Safar said, according to the official Syrian Arab News Agency.
The attacks Thursday killed at least 55 people. The government has blamed "terrorists," while members of the Syrian opposition have blamed the government.
Since the bombings, reports of bloodshed only continue to mount.
The Local Coordination Committees of Syria, an opposition network, reported at least four deaths Saturday. The dead include one person killed by regime sniper fire in Hama and one man who died from gunshot wounds sustained Friday after regime forces stormed his Deir Ezzor home, the group said.
Nine government soldiers were injured when two armored cars were targeted in clashes between Syrian forces and armed defectors in the village of Hantoteen, in Idlib province, the UK-based Syrian Observatory for Human Rights said.
A homemade bomb also blew up a military vehicle in Maerat Al Nouman in Idlib province, according to state-run Al Dounia television.
Late Friday, a powerful explosion rocked Syria's most populous city of Aleppo, killing a guard at an office of President Bashar al-Assad's ruling Baath Party, opposition groups reported.
The cause of the blast was not immediately known. Heavy gunfire was heard in its aftermath, the Syrian Observatory for Human Rights reported.
At least 20 people, including the Aleppo security guard, were killed across Syria on Friday, the observatory said.
Damascus and Aleppo have been the scene of a flurry of attacks in recent months. Aleppo, a commercial center and long a bastion of support for al-Assad, had been largely spared in Syria's 14 months of bloody uprising. But recent protests and violence there could signal a significant shift.
Syria's foreign ministry underscored the urban violence in identical letters to U.N. Secretary-General Ban Ki-moon and U.N. Security Council President Agshin Mehdiyev, who is the Azerbaijani ambassador to the United Nations.
The letters said that Damascus, Aleppo and other Syrian cities "witnessed several terrorist bombings over the last weeks" that left dozens of innocent people dead, SANA reported.
Syria blames "terrorists" for the attacks, a term it uses to describe the opposition and to rationalize security forces' crackdown.
Some analysts said the attacks raise concerns about the presence of jihadist elements in Syria, noting Thursday's Damascus strikes resemble suicide car bombings during the sectarian violence in Iraq in the past decade.
But opposition groups have said the regime is responsible for the violence that erupted after government forces began a crackdown on peaceful protests in March 2011. That fierce clampdown spurred a grassroots uprising against the regime.
The opposition Syrian National Council said al-Assad's regime staged Thursday's deadly suicide bombings in Damascus "to spur chaos, disrupt the work of the international observers and divert attention away from other crimes being committed by its forces elsewhere."
"In orchestrating such acts," the council said Friday, "the regime seeks to prove its claims of the existence of 'armed terrorist gangs' in the country that are hindering its so-called 'efforts of political reform.'"
The deadly blasts in Damascus took place near a military intelligence center.
But the council questioned how the attackers could have made it past security to conduct the bombings.
"The security branch is heavily guarded and surrounded with cement barriers at a distance from the exterior fence. It would be reckless to carry out such an attack, because it would in no way impact the security building," the group said.
Frequent reports of violence cast doubt on the effectiveness of a U.N.-backed peace plan that was agreed upon last month.
More than 1,000 people have died since the cease-fire was supposed to go into effect on April 12, according to the LCC.
CNN cannot independently verify reports of deaths and violence because the Syrian government has severely restricted access to international media.
A team of U.N. monitors is on the ground to observe the progress of the cease-fire and encourage the implementation of the peace plan.
At least 145 observers and 56 civilian staff were in Syria as of Friday, a U.N. spokesman said. About 300 observers are expected within weeks.