The U.S. military for the first time is putting together a plan to provide lethal defensive weapons to Ukraine to counter a growing Russian military menace to Ukraine and Europe.

The planning underway by the Joint Chiefs of Staff requires White House approval, which puts President Trump in a bind because it threatens to upend his hopes of improving relations with Russian President Vladimir Putin.

An official at the White House’s National Security Council told USA TODAY the U.S. government has not ruled out providing defensive weapons to Ukraine. The official requested anonymity because of the sensitive subject.

The issue is being debated in the White House as violence spikes in eastern Ukraine, where Russian-backed insurgents have stepped up attacks on Ukrainian government forces, and as Russia prepares for a large military exercise that analysts expect will put more tanks on the borders of Ukraine and NATO countries.

On Monday, Vice President Pence warned of the "specter of aggression" by Russia as he began a visit to the Baltic nation of Estonia, which worries about Russian threats. Estonia and two other former Soviet republics, Latvia and Lithuania, now belong to NATO.

The proposal to arm Ukraine comes as Trumps prepares to sign new legislation that strengthens sanctions on Russia over its involvement in neighboring Ukraine, a move that prompted Putin Sunday to expel 755 American diplomats.

The logic behind arming Ukraine, which the Kremlin opposes, was endorsed this week by Trump’s special representative to Ukraine, former NATO envoy Kurt Volker.

“Defensive weapons, ones that would allow Ukraine to defend itself, and to take out tanks for example, would actually help" stop Russia threatening Ukraine, Volker said in a BBC interview published Tuesday.

"I'm not again predicting where we go on this. That's a matter for further discussion and decision. But I think that argument that it would be provocative to Russia or emboldening of Ukraine is just getting it backwards," he said.

Nineteen Ukrainian troops have been killed and 65 injured in July in shelling, sniper fire and firefights, according to the Ukraine Crisis Media Center in Kiev.

After nine Ukrainian soldiers were killed in a series of attacks on July 19, State Department spokeswoman Heather Nauert blamed "so-called separatists" who she said are “Russian-led and Russian-backed."

Nauert said Russia’s military is in Ukraine leading and advising anti-government forces, a claim Putin has repeatedly denied. Secretary of State Rex Tillerson has not decided whether to recommend lethal aid to Ukraine, Nauert said Thursday.

Air Force Gen. Paul Selva testified before the Senate Armed Services Committee on July 18 that the Joint Chiefs of Staff and European Command are preparing a proposal to arm Ukraine.

"It will be more than just a military recommendation," Selva said. "This will be a policy choice on whether or not we're going to give the Ukrainian government the tools they need to defend themselves against what we believe to be a Russian-supported insurgency movement in the Donbass" region of eastern Ukraine.

Such planning marks a change in U.S. thinking about the conflict since it began in 2014, when President Barack Obama and German Chancellor Angela Merkel said more weapons would provoke a Russian escalation and military buildup.

“But the Russians are doing all this anyway,” and now threaten other NATO countries in eastern Europe, said Phillip Karber, a former Defense Department official under President Ronald Reagan who now heads the Potomac Foundation in Vienna, Va. “There’s a realization that there has to be a response, at least by the military.”

Karber has recommended in briefings on Capitol Hill and with defense and White House officials that the U.S. provide Ukraine with anti-tank weapons that would blunt an armored advance by Russia. Russia has reconstituted, moved or upgraded three large military units, which are now positioned near Russia’s western border, opposite Ukraine and U.S. allies in Eastern Europe, Karber said.

Russia brought back the First Guards Tank Army, which was disbanded after the Soviet Union collapsed in 1991, ending the Cold War. That unit is now manned with veteran professional soldiers rather than conscripts or reservists, and will be sent to Belarus, north of Ukraine, to take part in the military exercises that Russia holds every few years.

The Russian military recently moved the 20th Army, a combined infantry and mechanized unit, from near Moscow to near the Ukrainian border opposite the eastern Ukrainian city of Kharkiv, roughly midway between Ukraine’s north and south, Karber said.

And Russian’s 8th Army has been deployed near the Russian city of Rostov, near southeastern Ukraine. Two headquarters subordinate to the 8th Army are stationed in insurgent-held Donetsk and Luhansk in eastern Ukraine, Karber said.

Russia’s exercises, which date back to the Soviet era during the 1970s and 1980s, were revived in 1999 by Putin when he became prime minister, Karber said.

The last exercise took place in 2013, and involved a simulated attack on a NATO country and the simulated use of nuclear weapons. Russia ordered 200 railway cars to transport tanks for the drill.

This year, Russia ordered 4,000 rail cars to move the 1st Guards Army’s tanks to September’s exercise, Karber said.

“That will be the largest buildup since the Cold War and right up against the Baltics,” he said, referring to former Soviet republics Estonia, Latvia and Lithuania, now NATO members. “It’s a big deal.”

John Herbst, a former U.S. ambassador to Ukraine who is at the Atlantic Council think tank in Washington, D.C., joined Karber and former NATO commander Gen. Philip Breedlove at a recent event in Washington to urge arming Ukraine with defensive weapons.

If Trump’s special envoy Volker “wants a real shot at getting a change in this war, he has to raise the cost to the Kremlin,” Herbst said. He needs to “persuade the Kremlin that aggression is not a winning option,” he said.