U.S. President Donald Trump said he is ready to impose “major sanctions” on Moscow if NATO members stop purchasing Russian oil.

In a letter to alliance members, which he published on his social network Truth Social, Trump wrote: “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 added that oil purchases by NATO states have been “shocking,” arguing that it “greatly weakens your negotiating position, and bargaining power, over Russia.”

Trump said he believes ending Russian oil purchases, combined with the imposition of tariffs on China of 50 percent to 100 percent — by NATO members and the U.S. — would help bring an end to what he called a “ridiculous war.”

Trump, promised in his election campaign that he would end the war within a day, concluded his statement Saturday by saying that if NATO followed his plan, the war would “end quickly.”

Several European leaders expressed confidence in recent days that they had convinced Trump that Russian President Vladimir Putin is not interested in ending the war and has to be forced to the negotiating table, officials and diplomats told POLITICO.

In a flurry of diplomatic visits, the leaders have discussed new financial restrictions and plans to cut off the flow of Russian energy. Hungary and Slovakia, in particular, remain deeply reliant on Russian oil and gas.

Ukrainian President Volodymyr Zelenskyy applauded the moves toward increased sanctions on Moscow, saying reducing the consumption of Russian oil “will definitely reduce Russia’s ability to fight” its war in Ukraine.

“We can hear the position of the U.S., and this position should be heard by all who still choose supplies from Russia rather than from other partners,” Zelenskyy said in his nightly address on Saturday. “Anyone seeking an end to this war must take the necessary steps to halt Russia’s war machine,” he said.

Meanwhile, NATO member Romania said late Saturday that a Russian drone breached its airspace during an attack by Moscow on Ukraine — the second incursion into a NATO country’s skies in less than week. Russian drone flights into Polish airspace on Wednesday prompted NATO to bolster its eastern borders.

Romania’s defense ministry said in a statement Saturday that the country had scrambled two F-16 fighter jets to monitor the Russian airstrikes across the border and the pilots detected the drone in Romanian airspace. The drone didn’t fly over inhabited areas, and no damage or injuries were reported, the ministry said.

Romanian Foreign Minister Oana-Silvia Toiu said on X that the Russian drone was tracked in Romania’s airspace for 50 minutes before it left without causing any damage or casualties. “Two allied German Eurofighters were also ready in the air monitoring the situation,” she added.

“Such actions by Russia are unacceptable and reckless,” Toiu said.

Saturday’s incursion comes just days after about 20 Russian drones entered Poland’s airspace in the early hours of Wednesday morning — leading Warsaw to scramble fighter jets and invoke NATO’s Article 4.

This article has been updated.