Russia and the United States have agreed "all the documents" for a successor to the START nuclear disarmament treaty, a Kremlin source said on Wednesday.
"As of now, all the documents on the new START treaty have been agreed upon," said the Kremlin source, who spoke on condition he not be named.
Russia's ambassador to Prague, Alexei Fedotov, said meanwhile that the Czech capital had been chosen as the venue for signing the pact.
The comments indicated a possible breakthrough in long-running talks on replacing the landmark 1991 Strategic Arms Reduction Treaty, a key goal of the administration of US President Barack Obama.
Obama has made talks on replacing START the central element of his efforts to "reset" strained US-Russian relations, but they had reportedly been bogged down by disagreements over US missile defence.
Earlier on Wednesday, a US official, speaking in Washington on condition of anonymity, said the White House had spoken with Russia and the Czech Republic about its desire to sign the new treaty with Russia in Prague.
"Prague is indeed considered the most likely venue for the signing of the new START treaty," the Kremlin source also said.
Moscow and Washington have held months of difficult negotiations aimed at replacing the treaty, which expired in December.
Signed in 1991, START led to huge reductions in the US and Russian nuclear arsenals and imposed verification measures to build trust between the two former Cold War foes.