U.S. President Donald Trump said he raised the possibility of a nuclear deal involving the United States, Russia, and China during talks with Chinese leader Xi Jinping.

Trump told reporters he wants the three countries to sign a pact that would cap the number of nuclear warheads in each nation’s arsenal, according to The Associated Press.

Beijing’s arsenal, according to Pentagon estimates, exceeds 600 operational nuclear warheads and remains far from parity with the United States and Russia, which are each estimated to possess more than 5,000 nuclear warheads.

But Trump suggested Xi was receptive to the idea when he raised it during their private talks.

“I got a very positive response,” Trump said. “This is the beginning.”

The last nuclear arms pact between Russia and the United States, known as New START, expired in February, removing caps on the world’s two largest nuclear arsenals for the first time in more than half a century.