Syrian rebels fought deadly battles with government forces north of the divided city of Aleppo on Wednesday as both sides sought to expand their ground amid a push by the U.N. envoy to the country to broker a cease-fire in the war-ravaged city.

The clashes began with a government offensive launched few hours before the envoy, Staffan de Mistura, said that President Bashar Assad has expressed willingness to suspend bombing of Aleppo for six weeks.

The hiatus would set the stage for a proposed U.N. plan to "freeze" hostilities in what is Syria's largest city. However, rebels and opposition activists said that they are deeply skeptical -- based on past experience and similar peace efforts that have crumbled -- that the government would abide by any truce.

"The regime says it wants dialogue then attacks rebel positions," said Bahaa Halaby, an activist in Aleppo. He said fierce clashes were taking place north of the city Wednesday.

Syrian government forces backed by Shiite fighters, including the Lebanese Hezbollah group, launched a surprise offensive on Tuesday, capturing several villages that brought them closer to their goal of cutting off the main supply route to rebels in Aleppo and besieging opposition-held areas of the city.

More than a hundred people on both sides of the fighting were killed by Wednesday, in a counteroffensive in which rebels regained much of the territory they last a day earlier, activists said.

An amateur video released by rebels showed the bodies of at least 25 Syrian soldiers and pro-government gunmen in Aleppo's northern suburb of Mallah, scattered in a muddy open field. The video appeared genuine and corresponded to other Associated Press reporting of the violent clashes taking place.

Pro-government TV channels, in turn, ran footage showing troops running behind tanks in smoke-filled fields and fighters driving vehicles mounted with heavy machine guns to the backdrop of nonstop gunfire and explosions.

A few hours after the government offensive started Tuesday, de Mistura offered a glimmer of hope on his efforts to find a solution to Syria's civil war, telling the U.N. Security Council at a briefing that Assad had agreed to halt airstrikes and artillery shelling of Aleppo for a period of six weeks.

"Let's be frank, I have no illusions because based on past experiences this will be a difficult issue to be achieved," de Mistura said. He added, however, that he would return to Damascus "as soon as possible" to announce a start date.

Rebels claimed the government offensive proved Damascus was not serious, and said they have serious doubts about how a freeze in hostilities could take place in a city that was once Syria's commercial capital and is now a wasteland and mosaic of various rebel groups.

Hamed said he believed most rebel factions will abide by a truce if the government halts airstrikes and releases detainees, starting with female prisoners. Speaking via Skype, he and other Aleppo-based activists said militants from the Nusra Front -- Syria's Al Qaeda branch, which has a small presence in the city -- are not expected to abide by the plan.

The Islamic State group is also about 18 miles northeast of the city.

Still, there were signs that most rebel factions might be at least willing to engage on the plan, and see whether the government will make good on its pledge to de Mistura.

Two and a half years of fighting in the city has exhausted fighters and utterly destroyed rebel-held neighborhoods. What is left of the city's residents are looking for any relief from fighting.

"The most important thing for the opposition is a cease in the (government's) barrel bombs campaign in Aleppo," Hamed said, referring to large canisters packed with explosives and metal scraps that the Syrian army drops regularly from the air, causing widespread damage and casualties.

Another activist in Aleppo, Bahaa Halaby, said Syrian troops were trying to besiege rebel-held areas before any freeze goes into effect.

"The regime wants to implement the initiative after advancing on the ground," Halaby said via Skype.

Salem Al Meslet, a senior member of the opposition Syrian National Coalition, said Assad's regime "has violated every truce and agreement reached with the rebels in various areas and in the presence of international monitors."

"It shows, unequivocally, that Assad's regime cannot be presented as a partner in any political solution," he said in a statement.

The Britain-based Syrian Observatory for Human Rights and Turkey-based activist Bari Abdellatif said rebels regained control of the villages of Ratyan and Dweir Zeytoun early Wednesday. The Observatory says 70 troops and 86 rebels were killed in Tuesday's fighting.

The Observatory and Hamed, the Aleppo-based activist, said fighting is now concentrated in the village of Bashkoy, just north of Aleppo.

The Observatory and the Lebanon-based Al-Mayadeen TV said some 30 Syrian soldiers were able to reach the besieged, predominantly Shiite village of Zahraa north of Aleppo for the first time since 2012.

Activists denied that, adding that both that village and the nearby Nubul are still encircled by rebels.