BEIRUT, Lebanon -- Antigovernment activists in Syria said Scud missiles fired by the Syrian military slammed into at least three rebel-held districts of Aleppo on Friday, flattening dozens of houses, leaving at least 12 civilians dead and burying an undetermined number of others, perhaps dozens, under piles of rubble.
The assertion, corroborated by videos posted on the Internet, came one day after Syrian government targets in central Damascus were hit by multiple car bombings that were among the deadliest and most destructive so far in the nearly two-year-old conflict.
The reported attack on Aleppo's Hamra, Tariq al Bab and Hanano areas with Scuds, which are not known for their accuracy, was the second time this week that the Syrian opposition has accused the military of using such missiles on Aleppo's rebel-held areas.
Aleppo, the embattled northern city that was once Syria's commercial capital during more peaceful times, has become one of the focal points of rebellion in the uprising against President Bashar al-Assad. On Tuesday, according to activists in Aleppo, a Syrian missile leveled part of Jabal Badro, another neighborhood controlled by the rebels, killing at least 19 people.
The Syrian Observatory for Human Rights, a Britain-based group with contacts inside Syria, said in a statement that the victims of missile explosions in Aleppo on Friday included children and that the number of victims "is expected to rise significantly because there are dozens of wounded under the rubble."
There was no immediate mention of the Aleppo attacks by Syria's state-run media. The Web site of Syria's official SANA news agency was dominated by the aftermath of the car bombings that had hit central Damascus on Thursday and had left more than 70 people dead. The ferocity and scope of those bombings were unusual for central Damascus, which up until now has been largely insulated from much of the carnage and destruction wrought by the conflict in the outer Damascus suburbs and other parts of the country.
Most of the casualties in Damascus were caused by an especially powerful bomb near the headquarters of President Assad's Baath Party and the Embassy of Russia, which were both damaged, according to witnesses contacted inside Damascus and Russian news reports. SANA said a hospital and neighboring schools also were damaged.
No group has taken responsibility for the Damascus bombings but the government has said they were carried out by terrorists, its generic description of the alliance of armed rebels seeking to depose Mr. Assad. The National Coalition of Syrian Revolutionary and Opposition Forces, the main Syrian group for the opposition which was meeting in Cairo at the time, condemned the bombings, as did its Western supporters, including the United States.
Victoria Nuland, a State Department spokeswoman, told reporters on Thursday that the United States denounces such bombings as "indiscriminate acts of violence against civilians or against diplomatic facilities, which violate international law, and we continue to emphasize that perpetrators on all sides have to be held accountable."
Nonetheless, the bombings appeared to create a new source of diplomatic friction between the United States and Russia, which has consistently supported the Syrian government during the conflict and has rejected any proposed solution that would force Mr. Assad to relinquish power.
Russia's mission to the United Nations accused the United States of blocking its attempt to seek approval of a Security Council statement that would have condemned the Damascus bombings as terrorism. The United States mission denied the Russian accusation, saying it had only requested that the Russian statement include a paragraph that also condemned the Syrian government's "continued, indiscriminate use of heavy weaponry against civilians."
Erin Pelton, a spokeswoman for the United States mission, said in news release posted Friday on its Web site that "Unfortunately, if predictably, Russia rejected the U.S. suggested language as 'totally unacceptable' and withdrew its draft statement."
Other insurgency-related violence was reported by the Syrian Observatory and other activists elsewhere in Syria on Friday, including random sniping attacks in the north-central city of Raqqa that killed four people during an antigovernment demonstration, and seven people killed around a mosque in Dara'a, the southern city where the anti-Assad uprising first began in March 2011.
The Local Coordination Committees, an anti-Assad network of activists, reported that fighters from the Free Syrian Army and other groups had taken control of at least two military facilities in the suburbs of Deir al-Zour, the eastern city that has been a battleground for many months. The report, which could not be corroborated, also claimed that rebels had gained control of a missile facility in Deir al-Zour that was formerly the site of a partly built nuclear reactor bombed by Israeli warplanes in 2007. Syria disclosed the existence of the missile facility four years ago at a technical meeting of the International Atomic Energy Agency.
Activists reached via Skype also reported what they described as rival demonstrations in the city of Kafranbel in northern Idlib province, a rebel-held area, between a group calling for the establishment of an Islamic caliphate and a group seeking the establishment of a secular state. The demonstrations appeared to reflect the influence of militant Islamist insurgent groups like the Al Nusra Front, which have been welcomed by some in the Syrian opposition for their brave fighting skills but are regarded warily by others. The United States has been reluctant to provide weapons to the Syrian insurgency partly because it considers Al Nusra a terrorist group, with links to Al Qaeda militants in neighboring Iraq.
Idlib province also has been rived in recent weeks by a wave of retaliatory kidnappings between rival Shiite and Sunni villages, reflecting what appeared to be a deepening sectarian divide caused by the conflict. But in a possible sign of eased tensions, the Syrian Observatory reported on Thursday that scores of hostages had been released.
In Cairo, the Syrian opposition coalition concluded its two-day meeting on Friday with an announcement that it would convene again in Istanbul on March 2 and begin forming a provisional government by naming a prime minister. Members hope that such a government can begin providing services in rebel-controlled territories and help prepare for a transition, predicated on the assumption that Mr. Assad leaves power.
The coalition also pulled back from recent statements by its leader, Sheik Ahmad Moaz al-Khatib, opening the possibility of talks with members of Mr. Assad's government about a political solution to end the conflict.
"Bashar al-Assad and the security and military leadership responsible for the state of Syria today must step down and be considered outside this political process," the coalition said in a statement after the meeting. "They cannot be part of any political solution for Syria and must be held accountable for their crimes."
Hwaida Saad reported from Beirut, and Rick Gladstone from New York. David D. Kirkpatrick contributed reporting from Cairo.
This article originally appeared in The New York Times.