US President Donald Trump said Saturday he was ready to sanction Moscow, but on the condition that all NATO allies agree to completely halt purchases of Russian oil and implement their own sanctions.

He also suggested members of the transatlantic alliance consider slapping tariffs of 50 percent to 100 percent on China as a way to help end Russia's war in Ukraine.

"I am ready to do major Sanctions on Russia when all NATO Nations have agreed, and started, to do the same thing, and when all NATO Nations STOP BUYING OIL FROM RUSSIA," Trump said in a post on his Truth Social platform, which he described as a letter to all NATO nations and the world.

Trump has repeatedly threatened Russia with additional sanctions -- including last weekend after the Kremlin unleashed its biggest-ever aerial barrage against Ukraine -- as a way to hit at revenue Moscow needs for its grinding war.

But so far he has failed to follow through, frustrating Kyiv.

The president, who met his Russian counterpart Vladimir Putin last month at a summit in Alaska, branded NATO nations' purchase of Russian oil "shocking" and said it weakens their bargaining power over Moscow.

"Anyway, I am ready to 'go' when you are. Just say when?"

Trump also raised the prospect of NATO imposing tariffs on China, which is believed to have boosted strategic cooperation with Moscow and held a high-profile summit with Putin recently in Beijing.

"I believe that (NATO sanctions on Russia), plus NATO, as a group, placing 50% to 100% TARIFFS ON CHINA, to be fully withdrawn after the WAR with Russia and Ukraine is ended, will also be of great help in ENDING this deadly, but RIDICULOUS, WAR," Trump said.

"China has a strong control, and even grip, over Russia, and these powerful Tariffs will break that grip."

If the 32-member alliance "does as I say, the WAR will end quickly," Trump said. "If not, you are just wasting my time."