The UN says it 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.
It said it was ready to help an estimated 1.7 million people in hard-to-reach areas by the end of March.
A cessation of hostilities began on Saturday and there have been complaints of breaches from both sides.
But it otherwise appears to be intact with a key Syrian opposition group saying the situation is much better.
Western powers have accused Russia of attacking moderate rebels fighting Syrian President Bashar al-Assad; Moscow says it only targets UN-designated terror groups, foreign media reports.