However, the rebel alliance is a fractured collection of militiamen and freelance revolutionaries with no central leadership.
Opposition activists say the bombings, like the attacks in Damascus, are suspicious in part because the explosions successfully targeted heavily guarded security posts. Both vehicles in Aleppo managed to get close enough to cause extensive damage.
One activist who said he had been released this week after being held for two weeks at a military facility that was bombed Friday, said the gates were opened only after careful security checks. "There is no human who can come close because there are cement checkpoints," the activist said.
Despite Aleppo's pro-Assad reputation, the opposition says the protest movement has been growing there, a worry for the government.
After Friday's bombings, opposition activists said, protesters took to the streets in two neighborhoods, Fardous and Marje. In one case, authorities opened fire, killing at least 13, according to the Local Coordination Committees, an opposition coalition. It was one of the bloodiest protest clashes to date in Aleppo.
Reports indicated that the city was tense and that many were fearful the bombings could mean the violence raging elsewhere had finally arrived. Security was tightened. A witness reported that a security officer at a checkpoint asked all the men in a minibus if they were from Aleppo, apparently worried about infiltration.
Elsewhere in Syria, opposition activists reported that the government shelled the rebel strongholds of Homs and Zabadani, a town near the Lebanese border.
The opposition has reported hundreds killed in Homs in the last week. On Friday, the death toll from violence in Syria, not including the bombing victims in Aleppo, reached at least 64, according to the Local Coordination Committees. There was no way to verify the figure because much of Syria is off-limits to journalists.
Special correspondent Rima Marrouch contributed to this report.