Foreign Minister Sergei Lavrov warned U.S. lawmakers on Monday that any changes to the New START nuclear arms reduction treaty signed by Presidents Barack Obama and Dmitry Medvedev in April could kill the pact.

Lavrov's warning came as the White House pressed for a ratification vote on New START this week before the Senate breaks for Christmas.

Some U.S. Republicans want to make changes in the treaty, which they say could limit U.S. national security options, and to the accompanying ratification resolution before voting.

Democrats, whose Senate majority was reduced in congressional elections last month, have moved to bring the treaty to a vote this week before the new chamber takes office in January. It needs 67 votes for approval in the 100-member Senate.

"I can only underscore that the Strategic Nuclear Arms Treaty, worked out on the strict basis of parity, in our view fully answers to the national interests of Russia and the United States," Lavrov said in an interview with Interfax.

"It cannot be opened up and become the subject of new negotiations," he said.

Medvedev has told the State Duma not to ratify the pact until U.S. Senate approval comes through or is certain.

The Duma could potentially sign off on it this year if the Senate approves it in time, said Konstantin Kosachyov, chairman of the Duma's International Affairs Committee.

But he said Duma deputies would closely examine the U.S. ratification resolution and any declarations or notes accompanying it to ensure no significant changes were made.

"It's just impossible to say in what form we will ratify the pact without seeing the final Senate texts," Kosachyov said.

Lavrov also played down the potential effects of failure to ratify New START, saying improved U.S.-Russian relations were not "directly dependent" on the pact.

"Nuclear disarmament is one of the key areas but far from the only area of our cooperation with the United States, which has a much more multifaceted character," he said.

But he warned that recent improvements in Moscow's ties with NATO, which hit a low with Russia's brief war against NATO aspirant Georgia in 2008, were not "irreversible."

"The success of this process is not guaranteed," he said.