President Donald Trump on Sunday warned Russia that he may send Ukraine long-range Tomahawk missiles if Moscow doesn't settle its war there soon — suggesting that he could be ready to increase the pressure on Vladimir Putin's government using a key weapons system.

"I might say, 'Look: if this war is not going to get settled, I'm going to send them Tomahawks," Trump told reporters aboard Air Force One as he flew to Israel. "The Tomahawk is an incredible weapon, very offensive weapon. And honestly, Russia does not need that."

Trump said, "I might tell them that if the war is not settled — that we may very well." He added, "We may not, but we may do it. I think it's appropriate to bring up."

His comments came after Trump spoke by phone earlier Sunday with Ukrainian President Volodymyr Zelenskyy, and Trump said he mentioned possibly sending Tomahawks during that conversation.

"Do they want to have Tomahawks going in that direction? I don't think so," Trump said of Russia. "I think I might speak to Russia about that." He added that "Tomahawks are a new step of aggression."

His suggestions followed Russia having attacked Ukraine's power grid overnight, part of an ongoing campaign to cripple Ukrainian energy infrastructure before winter. Moscow also expressed "extreme concern" over the U.S. potentially providing Tomahawk cruise missiles to Ukraine.

Putin himself has previously suggested that the United States supplying long-range missiles to Ukraine will seriously damage relations between Moscow and Washington.

For his part, Zelenskyy described his latest call with Trump as "very productive," and said the pair had discussed strengthening Ukraine's "air defense, resilience, and long-range capabilities," along with "details related to the energy sector."

Trump in recent weeks has taken a notably tougher tact with Putin, after the Russian leader has declined to engage in direct talks with Zelenskyy about easing fighting.

Last month, Trump announced that he now believes Ukraine could win back all the territory lost to Russia — a dramatic shift from the Republican's repeated calls for Kyiv to make concessions to end Russia's war in Ukraine.

But the U.S. president, at least so far, has resisted Zelenskyy's calls for Tomahawks. The weapon system would allow Ukraine to strike deeper into Russian territory and put the sort of pressure on Putin that Zelenskyy argues is needed to get the Russians to seriously engage in peace talks.

Trump said aboard Air Force One of the war: "I really think Putin would look great if he got this settled" and that "It's not going to be good for him" if not.