For nearly a year now, the U.S. has spurned calls to provide arms to Ukraine in its increasingly bloody conflict with Russian-backed separatists.

But now, officials in the White House are musing openly about sending "lethal aid" to Ukraine, which some military analysts believe is the only way to deal with what they see as belligerence from Russian President Vladimir Putin.

Arming Ukraine "would be a very significant escalation, but it's a necessary one," says Stephen Blank, senior fellow with the American Foreign Policy Council in Washington, D.C., who calls Russia's actions in Ukraine "the greatest threat to international security that we have today."

'Any time a great power armed with thousands of nuclear weapons is backed into a corner, you are asking for really serious trouble.' - John Mearsheimer, University of Chicago

But there's a strong possibility that by arming Ukraine, the U.S. could spur Russia to unpredictable action, says John Mearsheimer, co-director of the Program on International Security Policy at the University of Chicago.

"People who are advocating that we up the ante by sending lethal aid to Ukraine are betting that this will cause Putin to throw up his hands and surrender," says Mearsheimer. "This is not going to happen."

U.S. Air Force Gen. Philip Breedlove, the top NATO commander, echoed this view on Thursday, saying that arming Ukraine "could trigger a more strident reaction from Russia."

German Chancellor Angela Merkel, for one, is opposed to arming Ukraine. She and French President Francois Hollande have drafted a new peace initiative that they are presenting in Ukraine's capital, Kyiv, on Thursday, and to Putin in Moscow on Friday.

Intensified fighting

Talk of a more concerted response from the U.S. and other NATO members comes after days of intensified fighting between Ukrainian troops and Russia-backed separatists in eastern Ukraine.

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Russian President Vladimir Putin continues to deny that his country has had any involvement in the current conflict in Ukraine, though Russia represents the separatist rebels in international negotiations.

According to the United Nations, more than 200 people have died there in the past three weeks. It is estimated that 5,000 people have died in the conflict to date.

On Wednesday, heavy shelling in the rebel stronghold of Donetsk killed at least five people and damaged a hospital and several schools, according to local officials.

It's been almost a year since Russia annexed Crimea and Russian-backed separatists started making incursions in eastern Ukraine, and a number of western commentators say it's time for the U.S. to help Ukraine, which is no match militarily for the Russian army on its own.

Editorials in media outlets such as USA Today and the Washington Post say giving Ukraine lethal weapons is the only solution to this conflict.

Russian Foreign Ministry spokesman Alexander Lukashevich said Thursday a U.S. decision to arm Ukraine would not only escalate the situation but "threatens the security of the Russian Federation."

U.S. Secretary of State John Kerry has said he is committed to finding a diplomatic solution, but he has also expressed concern about the increased presence of Russian tanks and artillery in rebel-held areas of Ukraine. Russia continues to deny any involvement in the conflict.

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U.S. Secretary of State John Kerry, right, was in Kyiv on Thursday to discuss solutions to the crisis with Ukrainian President Petro Poroshenko, left. (Efrem Lukatsky/Associated Press)

Stephen Blank says that up until now, all the Russian operations "have been conducted at a scale small enough so that they can pretend that they're not there," which is why NATO has been reluctant about getting involved.

"My belief is that if we let this go and not do what is necessary, we will face future challenges from Putin or others inspired by him," says Blank. "This has to be stopped sooner rather than later."

Testing Russian resolve

Any direct military aid from the U.S. would likely include armaments, intelligence information and "counter-battery radar," a mobile radar system that detects artillery projectiles, says William Courtney, a senior analyst at the Rand Corporation, a U.S. think tank.

Taras Kuzio, a senior researcher at the Canadian Institute for Ukrainian Studies, believes that if Ukraine, with the help of U.S. armaments, begins to defeat rebels on the ground, Russia would be compelled to send more of its own troops.

Then, Russia would no longer be in a situation of "essentially lying" about its presence on the ground, says Kuzio, because it would have to commit 50,000 to 100,000 troops.

He says that in this scenario, the U.S. would hope that a strengthened Ukraine army and significant casualties on the Russian side would break Putin's resolve.

"The American viewpoint is a bit like the 1980s, where the only way to get the Russians out of Afghanistan was to make them pay so much in terms of bodybags that eventually they say enough and they pull out, which they did," says Kuzio.

German Chancellor Angela Merkel

German Chancellor Angela Merkel does not condone arming Ukraine, and is scheduled to meet with Russian President Vladimir Putin in Moscow on Friday. (Tibor Illyes/Associated Press)

"We have to make the price sufficiently high for the Russians that eventually they recalculate their policies."

But Mearsheimer doesn't believe we will see a similar outcome in the current conflict.

He says Putin has already shown that economic hardships at home – such as depressed oil prices, a plunging ruble, western sanctions and the threat of a recession — are no obstacle to Russian military involvement.

And pressuring Putin on the battlefield will only rile him more, says Mearsheimer.

"Any time a great power armed with thousands of nuclear weapons is backed into a corner, you are asking for really serious trouble."