Syrian rebels launched an offensive aimed at breaking the government's siege of eastern Aleppo on Sunday, where the UN estimates some 300,000 people are trapped with dwindling food and medical supplies.
As the powerful, ultraconservative Ahrar al-Sham faction announced the rebels' campaign, residents in the northern city's besieged opposition quarters burned tires to reduce visibility for fighter jets flying overhead, according to local activist Wissam Zarqa.
The Britain-based Syrian Observatory for Human Rights, which gathers information from a network of local informants, said rebels and pro-government forces were clashing along several fronts on the outskirts of the divided city. Aleppo was Syria's largest city and its commercial capital before the war.
Presumed Russian or government jets bombed neighborhoods in the eastern side, the Observatory reported. Earlier in the day, helicopters dropped unguided barrel bombs on the opposition-controlled neighborhood of Bustan al-Basha, it said.
Government forces closed off the last route to the opposition holdout in early July, replicating siege tactics that it has employed with mixed results throughout the war.
Opposition neighborhoods in Homs, the country's third largest city, surrendered to government control in 2014 after a two-year siege left residents at the brink of starvation.
Other sieges have lasted until today, with devastating humanitarian consequences.
The UN's special envoy to Syria, Staffan de Mistura warned Friday that basic supplies in eastern Aleppo could run out in three weeks.
The Syrian and Russian militaries announced safe corridors for residents who wanted to leave the besieged area Thursday, but according to the Russian government, only 169 civilians had left by Saturday.
Several rights groups have warned that it is illegal to deprive civilians of basic necessities, and that residents should not have to choose between leaving their homes or starving.
In southern Syria, an airstrike on a hospital in an opposition-controlled town put the facility out of service Sunday.
The hospital in Jasem was targeted in one of several airstrikes to hit the town in Deraa province, located some 35 miles (57 kilometers) south of Damascus, according to the Local Coordination Committees activist network.
The group said six people were killed in the strikes, blaming them on the government.
The Syrian Observatory for Human Rights monitoring group said the hospital strike killed a pharmacist and put the facility out of service.
Hospitals are regularly targeted in Syria's war, drawing condemnation from the UN and the international community.
The New York-based Physicians for Human Rights says over 90 percent of attacks on medical facilities in Syria have been carried out by pro-government forces.
In the capital, Damascus, Ramzy Ramzy, the UN's deputy special envoy for Syria, reiterated the United Nations' intent to resume talks between the government and the opposition in late August, saying he discussed a political transition process with Foreign Minister Walid Moallem.
The opposition has demanded that President Bashar Assad step down, after the harsh government crackdown on protests in 2011 sparked a catastrophic civil war.
Whether the opposition and the international community will agree to have Assad rule during a transition period or beyond is a key sticking point in negotiations.
"The minister confirmed the intention of the Syrian government to participate in these talks once they are held," said Ramzy.
De Mistura was simultaneously meeting with the Iranian deputy foreign minister in Tehran, a close ally to the Damascus government.
Over a quarter million people have been killed in Syria's war.
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