(CNN) Would sending weapons to Ukraine block Russia from grabbing territory and stem violence in the volatile region? Or would it fuel further conflict and destabilize Europe?

That's a key issue Western leaders are weighing. And even as they tried to present a unified front at a press briefing Monday, it was clear that it's an area where U.S. President Barack Obama and German Chancellor Angela Merkel don't quite see eye to eye.

Obama said he hasn't decided yet whether to send arms to Ukrainian forces defending their country against Russian-backed separatists, and he hasn't set a deadline for when he will. But he insists it's an option that should be considered if diplomacy fails.

Any weapons the U.S. sends would not be meant to help Ukraine defeat the Russian army in an all-out battle, Obama said.

"Our goal has not been for Ukraine to be equipped to carry out offensive operations," he said, "but to simply defend itself."

Merkel said European diplomats are making "one further effort" at negotiating a deal. A key step is in the works: a possible meeting Wednesday between Russian President Vladimir Putin and Ukrainian President Petro Poroshenko.

"I've always said I don't see a military solution to this conflict," she said. "We have to put all our efforts in bringing about a diplomatic solution."

Obama and Merkel vow to work together

Both Obama and Merkel stressed the importance of working together.

"There may be some areas where there are tactical disagreements. There may not be. But the broad principle that we have to stand up for ... the principle of territorial integrity and sovereignty is one where we are completely unified," he said.

Western leaders cannot stand idly by "and simply allow the borders of Europe to be redrawn at the barrel of a gun," Obama said.

Merkel said the strong alliance between Europe and the United States would thrive despite any differences. Russia's incursions on Ukraine's borders, she said, are too dangerous for Europe to tolerate.

"I can only say that if we give up on this principle of territorial integrity of countries, then we will not be able to maintain the peaceful order of Europe that we've been able to achieve," she said.

Of course, those borders have already been redrawn once in the conflict. Last year, Ukrainian and U.S. officials say Russia flooded Crimea with troops ahead of its widely disputed annexation of the territory.

Russia has steadfastly denied accusations that it's sending forces and weapons into Ukraine. But top Western and Ukrainian leaders have said there isn't any doubt that Russia is behind surging violence and separatists' efforts to take over territory in eastern Ukraine.

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Hope on the horizon?

Representatives of Russia, Ukraine, Germany and France were making preparations Monday for a planned meeting Wednesday in Minsk, Belarus, to discuss efforts to reach a ceasefire.

If those talks fail, U.S. lawmakers will likely ratchet up pressure on Obama to send weapons to Ukraine.

But even that gathering, which could be a significant meeting between Putin and Poroshenko, isn't set in stone.

"We are planning for Wednesday if we succeed in settling the various points that we have discussed so intensively over these last days," Putin said Sunday.

The big challenge facing Putin, Poroshenko, Merkel and French President Francois Hollande is whether they can reach a peace agreement that will stick.

A peace agreement was signed in September in Minsk. It called for a drawback of heavy weapons, self-rule in the eastern regions and a buffer zone to be set up along the Russia-Ukraine border.

But the agreement quickly disintegrated, and the violence continued.

The new plan envisions a much broader demilitarized zone to run along the current front lines.

All the while, the crisis in Ukraine, which stemmed from a trade agreement , has killed more than 5,000 people, including many civilians.