The New START treaty, which caps the number of nuclear warheads well below Cold War limits, is set to expire in 2021 at a time of high tensions between Russia and the United States.

Pompeo said that Russia and the United States have both shown "large compliance" with New START -- unlike the separate INF treaty on medium-range missiles from which Washington this year said it would pull out, accusing Moscow of violations.

President Donald Trump "has made very clear that if we can get a good, solid arms control agreement, we ought to get one," Pompeo told the Senate Foreign Relations Committee when asked about extending New START.

But Pompeo said that the next START -- which stands for the Strategic Arms Reduction Treaty -- should include China, although he stopped short of describing Beijing's role as a condition.

"We need to make sure that we've got all of the parties that are relevant as a component of this as well," Pompeo said.

"It may be that we can't get there. It may be that we just end up working with the Russians on this. But if we're talking about a nuclear ... capability that presents risks to the United States, it's very different today in the world," Pompeo said.

Asked by Senator Jeff Merkley if he was referring to China, Pompeo replied in the affirmative and said that the rising Asian power had expanded its nuclear program.

Russia denied it was in violation of the INF, or Intermediate-Range Nuclear Forces, treaty and has described the US withdrawal from the signature Cold War pact as boding ill for extending New START.

Pompeo's hopes for extending New START mark a shift from 2017 when the newly elected Trump denounced it as a "one-sided deal" negotiated by his predecessor Barack Obama.