The United Nations is hoping that the truce brokered in Syria will provide a window of opportunity to distribute much needed aid in besieged areas.
Russian TV showed pictures of the Russian military distributing relief to a village near the border with Turkey.
The fragile cessation of hostilities, jointly drawn up by the US and Russia and unanimously endorsed by the UN Security Council, led to a dramatic drop in violence over the weekend – though rebels have accused the government of numerous violations.
Reuters reported on Monday afternoon that a senior official from Syria’s main opposition group the High Negotiations Committee (HNC) said the cessation of hostilities faced “complete nullification” because Syrian government attacks were violating the agreement.
Earlier, the UN Secretary General Ban Ki-moon, meeting his Special Envoy for Syria Staffan de Mistura in Geneva, said the ceasefire was largely holding.
De Mistura said he hoped to reconvene peace talks between government and opposition on March 7.
“We are working, we are working on that target, but it will of course depend on how the ceasefire, the cessation of hostilities holds, and on the humanitarian aid,” said the UN special envoy.
At the weekend the HNC warned that truce violations would render negotiations “unfeasible”.
The UN hopes to deliver food, water and medicine to six towns this week, reaching 150,000 people, and to help an estimated 1.7 million people by the end of March.
The UN High Commissioner for Refugees (UNHCR) estimates that thousands of people still risk death from starvation.