WASHINGTON, March 22 (Reuters) - China is "very carefully" watching how Washington and the world respond to Russia's invasion of Ukraine, but has not yet crossed the line of providing lethal aid to Moscow, U.S. Secretary of State Antony Blinken said on Wednesday.

Speaking on the heels of a visit to Moscow by Chinese President Xi Jinping, Blinken told a Senate hearing that if Russia was allowed to attack its neighbor with impunity, it would "open a Pandora's box" for would-be aggressors and lead to a "world of conflict."

"The stakes in Ukraine go well beyond Ukraine. ... I think it has a profound impact in Asia, for example," Blinken said, noting that Japan and South Korea had been major supporters of Ukraine in the conflict.

However, he said he did not believe that China has been providing lethal aid to Moscow.

"As we speak today, we have not seen them cross that line," Blinken told a Senate Appropriations subcommittee hearing, the first of four times he will testify to congressional committees this week.

Blinken testified later on Wednesday to the Senate Foreign Relations Committee.

Russia's invasion has led to debates over how the war will affect China's military thinking regarding Taiwan, the self-governing island that Beijing sees as sovereign Chinese territory.

"I think if China’s looking at this – and they are looking at it very carefully – they will draw lessons for how the world comes together, or doesn’t, to stand up to this aggression," Blinken said.

Xi and Russian President Vladimir Putin greeted one another as "dear friend" when they met in the Kremlin, and discussed China's proposals for a resolution to the Ukraine conflict.

"They have a marriage of convenience - I'm not sure if it's conviction. Russia is very much a junior partner in this relationship," Blinken said.

He said China's political and material support for Russia goes against Washington's interests.

Blinken told lawmakers that the State Department and the U.S. Agency for International Development (USAID) needs President Joe Biden's entire budget request - an 11% increase from last year - to face threats posed by Russia and China.

"The post-Cold War world is over, and there is an intense competition under way to determine what comes next," Blinken said.

The secretary of state urged every member of the International Criminal Court (ICC) to comply with an arrest warrant issued for Russian President Vladimir Putin.

The United States is not a party to the ICC.