Russia's lower house of parliament on Friday gave initial backing to a historic treaty with the US to slash the nuclear arsenals of the Cold War foes but warned final ratification would drag into next year.
The Russian lower house, the State Duma, voted with 350 in favour and 58 against for the new Strategic Arms Reduction Treaty (START) signed by Russian President Dmitry Medvedev and US President Barack Obama in April.
But hopes ratification could be wrapped up by the end of the year after the US Senate's approval on Wednesday were dashed when top Russian officials voiced unease at additions made by US lawmakers to their own ratification resolution.
Konstantin Kosachev, the head of the foreign affairs committee of the State Duma, said that the snag meant the parliament's ratification would now require two further readings that would now not take place until next year.
Lavrov told the debate before the vote that Moscow was "absolutely not in agreement" with an addition made by the US Senate that rejects a link between missile defence and strategic arms.
"This is an arbitrary interpretation of the principles of international law. The agreement, like any other, is a single whole," he said.
The Strategic Arms Reduction Treaty (START) restricts the former Cold War foes to a maximum of 1,550 deployed warheads each, a cut of about 30 percent from a limit set in 2002, and 800 launchers and bombers.
The US Senate on Wednesday approved the treaty after a months-long political battle, putting the ball firmly in the court of the Russian legislature to respond.
But prior to approving the treaty, US lawmakers attached non-binding amendments calling on Washington to deploy a missile defence system, modernise its nuclear arsenal and seek talks with Russia on curbing tactical nuclear weapons.
"We have no right to leave these interpretations without a response," said Kosachev. "They contradict the entire sense of the treaty."
The Duma's first reading vote only signifies approval of the original form signed by the presidents, forcing two more readings to discuss amendments or additions it may make.
"The second hearing will definitely not be held in this session but January at the earliest," said Kosachev. He said that the Duma would be recommending its own amendments in readings next year. "All of this takes time."
But officials emphasised that the despite the hitch over the additions, the Duma would still vote to ratify the pact, albeit with the amendments that it could add next year.
Although the ultra-nationalist Liberal Democratic Party and the Communists voted against the treaty, the dominance of pro-Kremlin ruling party United Russia means that the main doubt has been when, rather than if, parliament will ratify the accord.
"This is common sense," Lavrov said after the first reading vote. "Neither the US Senate nor the Duma took any actions that undermined the treaty," he said.
Obama and Medvedev had signed the agreement in April as part of a renewed US commitment to win both Russia's trust and cooperation in the handling of pressing international disputes.
Medvedev earlier hailed Obama as a man who keeps his promises, telling him to enjoy a rest after pushing through the Senate's ratification of a historic nuclear pact.
"He is a man who fulfils his promises. I wish my colleague a good rest, he did a quality job," the Kremlin chief said in a live end-of-year television interview.