A ceasefire in Syria brokered by Russia and the US is due to begin at sundown, though there are concerns over the its viability and after a weekend of government raids resulted in scores of civilian deaths.

The tentative truce, announced after marathon talks by the Russian and US foreign ministers last week, has cautiously reawakened hopes to end a five-year civil war that has killed hundreds of thousands of people and forced millions from the country.

The Free Syrian Army rebel group, a leading rebel alliance, said it would observe it from Monday sundown as agreed but with major reservations.

The alliance wrote to Washington on Sunday, saying that while they would "cooperate positively" with the ceasefire, they were concerned it would benefit the government.

Another leading rebel group Ahrar al-Sham, which is seen as a "terrorist group" both by the US and Russia, rejected the deal, saying it would only serve to strengthen the government of President Bashar al-Assad.

Widely supported

State news agency SANA reported on Saturday that Assad's government "approved the agreement" for a truce.

Lebanese Shia movement Hezbollah, which has intervened militarily in the war on behalf of Assad, announced its support.

Key Assad and Hezbollah backer Iran also welcomed the deal, though foreign ministry spokesman Bahram Ghasemi cautioned its success would rely on creating "a comprehensive monitoring mechanism, in particular control of borders in order to stop the dispatch of fresh terrorists" to Syria.

Ahead of the ceasefire, ruinous violence killed many people in several parts of the country, particularly in government air raids, as the sides appeared to be trying to strengthen their positions on the eve of the ceasefire.

More than 100 people were killed in a series of bombing raids, including on rebel-held parts of Aleppo province in the north of the country, and in Idlib in the northwest, Al Jazeera correspondents reported from the country.

The worst strikes were in Idlib city, the capital of the province of the same name, where they hit a market, killing 55 civilians.

Source: Al Jazeera And Agencies