Secretary of State Marco Rubio said on Sunday that a peace deal between Russia and Ukraine needs to happen soon, adding that the Trump administration will spend the coming week trying to determine whether to continue as a mediator.

"It needs to happen soon. We cannot continue to dedicate time and resources to this effort if it's not going to come to fruition," Rubio told NBC's "Meet the Press" program.

"This week is going to be a really important week in which we have to make a determination about whether this is an endeavor that we don't want to continue to be involved in, or if it's time to sort of focus on some other issues," he said.

Rubio spoke a day after President Donald Trump and Ukrainian leader Volodymyr Zelenskyy met in Rome during the funeral of Pope Francis to revive faltering efforts to end Russia's war with Ukraine.

Zelenskyy said the meeting could prove historic if it delivers the kind of peace he is hoping for, and a White House spokesperson called it "very productive."

Rubio said Washington has held off imposing sanctions on Russia to allow diplomacy to work but warned that Trump has options for dealing with any party that resists a peace deal.

"If it doesn't happen, it doesn't come to fruition, then as a nation state, there are options that we have for those who we hold responsible for not wanting the peace," the secretary of state said. "But we prefer not to get to that stage yet, because we think it closes the door to diplomacy."

U.S. Senate Minority Leader Chuck Schumer said on Sunday that he worries that Trump will "cave in to Putin."

"To just abandon Ukraine, after all the sacrifice that they made, after so much loss of life, and with the rallying of the whole West against Putin, it would just be a moral tragedy," Schumer said on CNN's "State of the Union."

Schumer said siding with Russia in the conflict would tear apart alliances with Europe and embolden dictators around the world.

Russia launched a sweeping drone assault and airstrikes across Ukraine overnight into Sunday, killing at least four people, officials said, after Trump cast doubt over Russian Putin’s willingness to end the war.

Three people died and four were wounded Sunday morning in airstrikes on Kostyantynivka in the Donetsk region, the regional prosecutor's office said. Another person died and a 14-year-old girl was wounded in a drone attack on the city of Pavlohrad in the Dnipropetrovsk region, which was hit for the third consecutive night, local Gov. Serhii Lysak said.

The attacks came hours after Russia claimed to have regained control over the remaining parts of the Kursk region, which Ukrainian forces seized in a surprise incursion last August. Ukrainian officials said the fighting in Kursk was still ongoing.

Trump said Saturday that he doubts Putin wants to end the more than three-year war in Ukraine, expressing new skepticism that a peace deal can be reached soon. Only a day earlier, Trump had said Ukraine and Russia were “ very close to a deal.”

“There was no reason for Putin to be shooting missiles into civilian areas, cities and towns, over the last few days,” Trump wrote in a social media post as he flew back to the United States after attending Pope Francis’ funeral at the Vatican, where he met briefly with Zelenskyy. Trump also hinted at further sanctions against Russia.

The Trump-Zelenskyy conversation on the sidelines of the pope’s funeral was the first face-to-face encounter between the two leaders since they argued during a heated Oval Office meeting at the White House in late February.

Russia fired 149 exploding drones and decoys in the latest wave of attacks, the Ukrainian air force said, adding that 57 were intercepted and another 67 jammed.

One person was wounded in drone attacks on the Odesa region and one other in the city of Zhytomyr. Four people were also wounded in a Russian airstrike on the city of Kherson on Sunday morning, according to local officials.

Russia’s Defense Ministry said Sunday that air defenses shot down five Ukrainian drones in the border region of Bryansk, as well as three drones over the Crimean peninsula, which was illegally annexed by Russia in 2014.

Five people were wounded when Ukrainian forces shelled the city of Horlivka in the partially occupied Donetsk region, the city’s Russian-installed Mayor Ivan Prikhodko said.

Material from the Associated Press was also used in this story.