Russian President Vladimir Putin offered Thursday to immediately extend the only remaining nuclear arms reduction pact with the United States, but a senior U.S. official said Washington wants a broader deal involving China.

Speaking at a meeting with military officials, Putin said that Russia has repeatedly offered the U.S. to extend the New START treaty that expires in 2021 but that it hasn’t heard back.

“Russia is ready to extend the New START treaty immediately, before the year’s end and without any preconditions,” he said.

The pact, which was signed in 2010 by U.S. President Barack Obama and then Russian President Dmitry Medvedev, limits each country to no more than 1,550 deployed nuclear warheads and 700 deployed missiles and bombers. The treaty, which can be extended by another five years, envisages a comprehensive verification mechanism to check compliance, including on-site inspections of each side’s nuclear bases.

Its expiration would remove any limits on Russian and U.S. nuclear arsenals for the first time in decades.

Arms control advocates have argued that the failure to extend the pact would be highly destabilizing at a time when Russia-U.S. relations have sunk to the lowest levels since the Cold War.

Read more: yahoo