US President Donald Trump issued a letter to NATO nations on Saturday, urging them to stop buying Russian oil and impose major sanctions on Russia to end its 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,” he said in a social media post.

He proposed that NATO, as a group, place 50-100 percent tariffs on China to weaken its economic grip over Russia.

This follows Trump’s earlier threats of sanctions on Moscow and secondary sanctions on countries buying its oil, such as top buyers China and India, if no progress is made to end the war in Ukraine.

The president has imposed an additional 25 percent tariff on Indian goods, citing its continued imports of Russian oil, but has not taken similar action against China.