The United Nations plans to deliver aid to about 150,000 Syrians in besieged areas over the next five days amid a partial truce in the country's civil war, the UN has said.
The UN said it will help an estimated 1.7 million people in hard-to-reach areas by the end of March, BBC reported.
A cessation of hostilities began in Syria on Saturday and there were complaints of breaches from both sides.
But it otherwise appears to be intact with a key Syrian opposition group saying the situation was much better.
Western powers have accused Russia of attacking moderate rebels fighting Syrian President Bashar al-Assad, but Moscow said it only targets UN-designated terror groups.
This is now a crucial window of opportunity for the UN to get food and aid to the besieged.
The truce does, in general, remain intact despite both the Western-backed opposition and regime sides complaining of dozens of violations over the weekend, including air strikes around Aleppo.
But it was not clear whether the target was the Al-Qaeda-linked Nusra front, which would not constitute a ceasefire breach since the group and Islamic State (IS) were not included in the deal.
A rebel spokesman talked of violations "here and there" but a situation much better than before. Moscow also complained of incidents but said on the whole, the ceasefire was being implemented.
There was still a lot of scepticism that it can continue for the full two weeks, Moscow said.
The UN's humanitarian coordinator in Syria, Yacoub el-Hillo, called the truce "the best opportunity that the Syrian people have had over the last five years for lasting peace and stability".
The organisation plans to use the lull to deliver food, water and medicine to towns like Madaya, where residents have reportedly been starving to death.
It said it needs the approval of Syria's warring parties before it can further expand its deliveries.
Efforts to deliver aid to Islamic State-besieged Deir al-Zour by air last week failed when several pallets were damaged, disappeared or landed in no-man's land.
"Primarily we will try to deliver food by land because that is the most efficient way, it's the way that we can deliver the largest amounts of food but there are some areas of the country where we can't get across the front line," Greg Barrow, a spokesman for the UN World Food Programme, said.
Almost 500,000 people live under siege in Syria, the UN estimated.
More than 250,000 Syrians have been killed and a million injured due to more than five years civil war in the country.
Around 11 million people were forced from their homes, of whom four million have fled abroad -- including growing numbers who are making the dangerous journey to Europe.
