Deputy Foreign Minister Grigory Karasin's statement follows a warning from the Russian ministry that South Ossetia is on the brink of a large-scale military conflict, and Moscow's claim that Georgia is aggravating the situation through excessive use of force. At least six people were killed late on Friday and early on Saturday in clashes between South Ossetian and Georgian forces.
Karasin, speaking after a phone conversation with U.S. Assistant Secretary of State Daniel Fried, said: "The Russian side expressed deep concern over the latest surge in tensions around South Ossetia, the unlawful buildup of Georgia's military presence in the region, and the intensive construction of fortifications."
"Russia has already urged Tbilisi to take a responsible approach, and it also counts on constructive cooperation from Washington," he said.
Last month, U.S. State Secretary Condoleezza Rice visited Georgia, and assured President Mikheil Saakashvili that Washington would help the country resolve its tensions with South Ossetia and Georgia's other rebel region, Abkhazia.
The U.S. will be joining Russia and Germany at UN-mandated peace talks in Berlin on August 15 on the Abkhazian and South Ossetian conflicts.
South Ossetia has evacuated more than 1,000 children across the border into Russia since violence broke out on Friday. The separatist authorities say six people were killed and 15 injured in mortar and sniper attacks from Georgian forces. Georgia had denied using snipers, and says it only retaliated against South Ossetian grenade attacks.
On Sunday, a total of 543 evacuees arrived in Russia's North Ossetia, and over 500 are expected to arrive by Monday evening.
South Ossetia's Interior Ministry said on Monday that Georgia had deployed a howitzer battalion and two mortar batteries along the border over the weekend, while police posts on the southern outskirts of the separatist republic's capital, Tshinvali, had come under sniper fire.
South Ossetian President Eduard Kokoity said on Sunday that the province was prepared to announce a general mobilization to repel Georgian attacks.
Russia has stepped up its support for Georgia's rebel provinces in recent months, angering Georgia's pro-Western leadership, which has set bringing the regions back under central control as a priority task.
South Ossetia declared its independence from Georgia following the collapse of the Soviet Union in 1991. Hundreds died in the conflict that followed.