KHERSON, Nov 15 (AFP) - Kyiv welcomed reported Chinese comments criticizing threats to use nuclear weapons as world leaders gathered in Indonesia to take part in Tuesday's G20 meeting, with Russia's invasion of Ukraine in the spotlight.

U.S. President Joe Biden and Chinese President Xi Jinping "underscored their opposition to the use or threat of use of nuclear weapons in Ukraine," the White House said in a readout of a meeting in Indonesia between the two leaders on the eve of the summit.

A readout of the Biden-Xi meeting on China's foreign ministry website made no use of the word "nuclear" but said: "Conflicts and wars produce no winner... and... confrontation between major countries must be avoided."

Russian President Vladimir Putin has repeatedly suggested Russia could use nuclear weapons to defend its territorial integrity, interpreted in the West as an implicit threat to use them over lands Moscow claims to have annexed.

Xi and Putin have grown close in recent years, bound by their shared distrust of the West, and China has refrained from publicly criticizing Russia for the invasion or from calling on it to withdraw its troops.

Zelenskiy, who had earlier visited Kherson, the biggest prize his troops have recaptured since the invasion began in February, welcomed Monday's remarks.

"It is important that the United States and China jointly highlighted that the threats of using nuclear weapons were unacceptable," Zelenskiy said in a late Monday address. "Everyone understands to whom these words are addressed."

Zelenskiy is due to address the G20 summit via video link on Tuesday.

In Turkey, meanwhile, U.S. and Russian spy chiefs met in the first known high-level, face-to-face contact of the war between the two countries.

To help avoid conflict escalation, CIA Director William Burns met on Monday with Russian foreign intelligence chief Sergei Naryshkin to convey the consequences should Putin use nuclear weapons, a White House spokesperson said.

The Kremlin confirmed a U.S.-Russia meeting had taken place in Ankara but declined to give details.

"The Ukrainian side views these talks with a maximum of realism," Ukrainian presidential adviser Oleksiy Arestovych said in an online video.