The United States and Russia have agreed to extend a cessation of hostilities in Syria to include Aleppo province and will coordinate to strengthen monitoring of the new arrangement, the State Department said on Wednesday.

It is critical that Russia redoubles efforts to press Syrian President Bashar al-Assad to comply with the new arrangement while Washington does its part with Syrian opposition forces, department spokesman Mark Toner said in a statement.

"Our objective remains, and has always been, a single nationwide cessation of hostilities covering all of Syria - not a series of local truces," Toner said.

Since the cessation of hostilities went into effect at midnight in Syria, "we have seen an overall decrease in violence in these areas, even though there have been reports of continued fighting in some locations," Toner said.

Aleppo has been the scene of the worst surge in fighting in recent days, wrecking the first major ceasefire of the five-year-old civil war, sponsored by the United States and Russia, which had held since February.

U.N. Syria envoy Staffan de Mistura met with U.S. Secretary of State John Kerry in Geneva on Monday and Russian Foreign Minister Sergei Lavrov in Moscow on Tuesday.

Upon returning to Washington on Tuesday, Kerry said he believed a cease-fire deal could still be restored in Syria despite escalating violence and warned Assad of "repercussions" unless he sticks to the agreement.

Kerry said it would take a few days until commanders in the field had been notified and the truce took effect.