Syria's main opposition High Negotiations Committee has blasted the government's offensive in Aleppo, and urged the international community to step up pressure on the government to comply with the ceasefire.

The remarks came after a meeting between the opposition group's head and UN Special Envoy for Syria, Staffan de Mistura, as part of the peace talks on Friday.

"You have heard of the attack carried out by the government. This is what it usually does before every round of talks. The government is sending a strong message that it doesn't want a political solution, but a military solution that will bring destruction to the whole country," said Assad Al-zoubi, head of Syria's main opposition group HNC.

UN mediator Staffan de Mistura has said a political transition would be the main focus of the current round of the peace talks in Geneva. More than 250,000 people have been killed in the 5-year-old conflict in Syria.

The thorniest issue remains on the fate of Syrian President Bashar al-Assad. Russia and the United States disagree on Assad's future, but have jointly pressed the Syrian government and the opposition to attend the indirect peace talks.