A Kremlin official has said that a bilateral agreement with Washington on adoptions is still in place, creating uncertainty over the immediate impact of Russia's new ban on US citizens adopting Russian children.

Russian President Vladimir Putin approved the ban from Jan 1 as part of a law passed to retaliate against legislation in the United States intended to punish Russian human rights abusers.

Moscow had told Washington it was also terminating a bilateral agreement regulating adoptions - but Putin's spokesman on Thursday said a technicality meant the agreement would have to remain in force until the beginning of 2014.