GENEVA (Reuters) - Rebel commanders in Syria said on Friday they still backed U.N.-mediated peace talks but accused the Damascus government of trying to shatter a ceasefire deal and urged world powers to judge whether it remained viable.

Syrian government air strikes hit rebel-held areas north of the city of Homs for a second day on Friday after a surge in fighting around Aleppo challenged the fragile cessation of hostilities deal agreed in February.

The bombardments came after the United Nations started a new round of peace talks in Geneva in which the Syrian government delegation was to meet the U.N. special envoy on Syria later on Friday.

“If we didn’t have faith as the Free Syrian Army, then we wouldn’t be here,” said Abu Osama al-Jolani, a senior commander in the southern rebel alliance.

“We are here in Geneva for this political process,” he said, flanked by other FSA commanders from southern and northern rebel units as well as the political leader of the powerful Saudi-backed Jaysh al-Islam, Mohammed Alloush.

The Free Syrian Army (FSA) is a loose alliance of groups, most of them with a Syrian nationalist outlook, that are often led by Syrian army defectors but lack central command structure.

“We are keen on this political solution, but it is the regime that is trying to destroy this truce,” Jolani said.

“Until now we are waiting on those (world powers) who made decisions for the truce to start to make a decision about it,” he said when asked if he believed the cessation of hostilities was still effective.

The government and rebels have traded accusations of blame for ceasefire violations.

The government and its allies have launched several major offensives in the Aleppo area, cutting the rebels’ shortest supply line to Turkey in February. Yet rebels still control territory around the city, including its western approaches.

Fighting near Aleppo has been escalating for two weeks, mostly to the south of the city where government forces backed by Lebanon’s Hezbollah and other militias have been waging fierce battles with rebels including the Nusra Front.

The al Qaeda-linked Nusra Front and Islamic State groups are not included in the cessation of hostilities agreement.

Iyad Shamsi, a commander in the FSA’s northern forces, said they were facing a three-pronged attack from different directions by government-backed forces, Islamic State and Kurdish YPG troops.

“What’s happening in Aleppo is a violation of the truce by the regime. The battles are fierce and this may lead to the biggest humanitarian tragedy in the world,” he said.

Shamsi said that if the Castello road, a key supply route for rebels into Aleppo, were cut off, then more than 1 million inhabitants would be besieged.