The main Syrian opposition group taking part in the negotiations with the Syrian government said on Tuesday that a truce on the ground had failed and it would keep out of talks indefinitely.
"The situation is not an easy one and of course it causes a certain degree of our concern," Kremlin spokesman Dmitry Peskov said, Reuters reported.
Staffan de Mistura, the United Nations mediator, said on Monday that the coalition delegation would stay in Geneva, but postpone its formal participation in the negotiations.
In February, the United States and Russian-brokered cease-fire brought weeks of relative calm to much of Syria, but appears to be breaking down across the north, where rebels have launched an offensive they claim is in retaliation for government breaches.