President Donald Trump upped pressure on Russia to “stop the killing” in Ukraine within 50 days, warning Tuesday that his threatened economic penalties against Moscow and its trading partners would be devastating.

Trump said yesterday he would impose secondary tariffs of up to 100 percent on countries that still trade with Russia in an effort to force the Kremlin to the negotiating table with Ukraine, giving Moscow until early September to respond.

A bill by Republican Sen. Lindsey Graham of South Carolina and Democratic Sen. Richard Blumenthal of Connecticut that has 85 Senate co-sponsors would authorize the president to impose secondary tariffs of at least 500 percent on imported goods from countries such as China, Brazil and India.

“They are very biting. They are very significant. And they are going to be very bad for the countries involved,” Trump told reporters at Joint Base Andrews in Maryland.

“They will be very, very powerful and very bad for the countries involved, and I hope we don’t have to pull that string and maybe we won’t, we’ll see,” he said.

Trump’s efforts to convince Russia to end its grinding three-year invasion of Ukraine, including multiple phone calls with Russian President Vladimir Putin and U.S.-led summits with Russian officials in Istanbul and Riyadh, have so far amounted to little, with the Kremlin’s missiles continuing to rain down on Ukrainian cities.

Last month, Russia hit Ukraine with 537 drones and missiles in Moscow’s most ferocious attack of the war, according to the Ukrainian Air Force.

The slow pace of the negotiations has appeared to irritate Trump, who repeatedly said during the campaign that he would quickly end the war in Ukraine.

“So far, it’s all talk and no action,” Trump said, referring to his conversations with Putin.

“Actually, Vladimir called me up. He said, ‘I’d love to help you with respect to making a deal with a couple of ‘em like Iran.’ I say, ‘Vladimir, I only want help with one deal: Russia. Because you’re the only deal that we’re not doing too well on.’”

Trump said he believed the Russian leader was being truthful when he claimed to want peace. “I hope he does, we’re gonna find out soon, and it could be before the 50 days,” Trump said.

With Putin rebuffing his efforts to end the war, Trump has gradually moved closer to the European position on arming Ukraine. During an Oval Office meeting with NATO Secretary-General Mark Rutte on Monday, the Republican leader announced that NATO allies will finance the purchase of U.S.-manufactured Patriot missile defense systems and other weapons for Ukraine.

“They’re already being shipped. They’re coming in from Germany and then replaced by Germany, and in all cases, the United States gets paid back in full,” Trump said Tuesday.

“NATO is gonna pay us back for everything. In some cases, we’re gonna be paid back by countries of the European Union directly,” he added. “But we’re always getting our money back in full.”

Jacob Wendler contributed to this report.