WASHINGTON — President Donald Trump on Monday threatened Russia with steep tariffs and announced a rejuvenated pipeline for American weapons to reach Ukraine, hardening his stance toward Moscow after months of frustration about unsuccessful negotiations for ending the war.

The latest steps reflect an evolving approach from the Republican president, who promised to swiftly resolve the war started by Russian President Vladimir Putin when he invaded Ukraine three years ago. Trump once focused his criticism on Ukrainian President Volodymyr Zelenskyy, whom he described as unwilling to compromise, but more recently has expressed growing irritation toward Putin.

“My conversations with him are very pleasant, and then the missiles go off at night,” Trump said. He complained that “it just keeps going on and on and on.”

Trump said he would implement “severe tariffs” unless a peace deal is reached within 50 days. He provided few details on how they would be implemented, but he described them as secondary tariffs, meaning they would target Russia’s trading partners in an effort to isolate Moscow in the global economy.

In addition, Trump said European allies would buy “billions and billions” of dollars of U.S. military equipment to be transferred to Ukraine, replenishing the besieged country’s supplies of weapons. He made the announcement in the Oval Office alongside NATO Secretary-General Mark Rutte.

Included in the plan are Patriot air defense systems, a top priority for Ukraine as it fends off Russian drones and missiles.

Doubts were recently raised about Trump’s commitment to supply Ukraine when the Pentagon paused shipments over concerns that U.S. stockpiles were running low.

Rutte said Germany, Finland, Canada, Norway, Sweden, the United Kingdom and Denmark would be among the buyers to supply Ukraine. He said “speed is of the essence here,” and he suggested that some weapons would be rushed to Ukraine and later replaced with purchases from the U.S.

Trump has long boasted of his friendly relationship with Putin, and he repeatedly asserted that Russia was more willing than Ukraine to reach a peace deal. He also accused Zelenskyy of prolonging the war and called him a “dictator without elections.”

But Russia’s relentless onslaught against civilian areas of Ukraine wore down Trump’s patience. In April, Trump urged Putin to “STOP!” launching deadly barrages on Kyiv, and the following month said in a social media post that the Russian leader “has gone absolutely CRAZY!”.

While Rutte was in Washington, Trump’s special envoy to Ukraine and Russia, retired Lt. Gen. Keith Kellogg, met with Zelenskyy in Kyiv.

Zelenskyy said he had “a productive conversation” with Kellogg about strengthening Ukrainian air defenses, joint arms production and purchasing U.S. weapons in conjunction with European countries, as well as the possibility of tighter international sanctions on the Kremlin.

“We hope for the leadership of the United States, because it is clear that Moscow will not stop unless its … ambitions are stopped by force,” Zelenskyy said on Telegram.

Russia has pounded Ukrainian cities, including the capital, Kyiv, with hundreds of drones and cruise and ballistic missiles that Ukraine’s air defenses are struggling to counter. June brought the highest monthly civilian casualties of the past three years, with 232 people killed and 1,343 wounded, the U.N. human rights mission in Ukraine said.

At the same time, Russia’s bigger army is making a new effort to drive back Ukrainian defenders on parts of the 620-mile front line.