NATO Secretary-General Jens Stoltenberg called Thursday on the United States and Russia to extend a major nuclear arms agreement before it expires in less than two weeks, and to later broaden the pact to include more weapons and China, Reuters reported.

The New START treaty, signed in 2010 by U.S. President Barack Obama and Russian President Dmitry Medvedev, expires on Feb. 5.

“We should not end up in a situation with no limitation on nuclear warheads, and New START will expire within days,” Stoltenberg told reporters in Brussels.

Russian Foreign Minister Sergey Lavrov signaled on Monday that Moscow is ready to move quickly to keep the pact alive, and U.S. President Joe Biden, who was Vice President when it was signed, has also spoken in favor of preserving it.

But Stoltenberg also underlined that “an extension of the New START is not the end, it’s the beginning of our efforts to further strengthen arms control.”

“We need to look at ways to include more weapons systems, systems not covered by the New START, but also to include China because China is now heavily modernizing their nuclear weapons, and not only modernizing but expanding their nuclear capabilities,” he said.