BEIRUT — A suicide bomber blew himself up at the gates of a Syrian prison Thursday and rebels stormed in, freeing hundreds of inmates as part of an offensive aimed at capturing key government symbols around the northern city of Aleppo, activists said.
Government forces, meanwhile, dropped crude ‘‘barrel bombs’’ in deadly airstrikes as both sides escalated their fight for the strategic city ahead of a second round of peace talks set for next week. Opposition leaders threatened to suspend the talks over the barrel bombings.
In the past six days alone, the makeshift weapons — containers packed with explosives, fuel, and scrap metal — have killed more than 250 people in Aleppo, including 73 children, according to Britain’s Syrian Observatory for Human Rights.
They include at least 11 who died Thursday — six of them from the same family — in the opposition-held neighborhood of Masaken Hanano. Videos uploaded by activists showed the aftermath, including men weeping amid ravaged buildings and corpses covered with blankets on the pavement.
In other developments, Syrian President Bashar Assad’s government said it has reached an agreement with the United Nations to let hundreds of trapped civilians leave besieged parts of the city of Homs and permit UN humanitarian relief convoys to enter.
In Washington, State Department spokeswoman Jen Psaki welcomed the agreement, which is expected to be carried out on Friday, but warned: ‘‘We should not be giving credit to a regime just for providing food for a few days to people who are starving, given that’s the right moral thing to do.’’
The rebels in Aleppo declared a push to seize the city’s central prison and the Kweiras military air base to the east. Opposition fighters have been trying to capture the installations for months.
Thursday’s offensive began when a Chechen suicide bomber from the Al Qaeda-linked Nusra Front attacked the prison gates, according to the Observatory.
Rebel fighters then managed to gain control of large parts of the compound. By evening, heavy clashes between the rebels and soldiers were raging inside.
The Observatory and other activists said the rebels freed several hundred prisoners.
State-run Syrian television said the army foiled an attempt by ‘‘terrorist groups’’ to attack the prison.
The nearly 3-year-old uprising against Assad has left more than 130,000 people dead and forced more than 2.3 million to seek refuge abroad.
The Syrian government has not said whether it plans to take part in the proposed new round of UN-hosted peace negotiations in Geneva, although its chief ally, Russia, expressed confidence earlier this week that the government would indeed return.
Michel Kilo, a senior opposition figure and member of the negotiating team, said he and other figures were discussing suspending the peace talks until the government halts its ‘‘hysterical’’ use of barrel bombs.