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Pablo Martinez Monsivais, Associated Press
President Barack Obama and German Chancellor Angela Merkel walk in together to begin their joint news conference in the East Room of the White House in Washington, Monday, Feb. 9, 2015. The leaders were expected to discuss the ongoing conflict in Ukraine, and arming Ukrainian fighters to wage a more effective battle against Russian-backed separatists.

WASHINGTON — President Barack Obama and German Chancellor Angela Merkel declared Monday that Russian aggression in Ukraine has only reinforced the unity of the U.S. and Europe, as they weighed the prospects of reviving an elusive peace plan to end the conflict.

Still, Obama held open the prospect that if a new round of diplomacy this week fails, the U.S. could send Ukraine's beleaguered military defensive weaponry. The president said that while he has yet to make a decision on lethal aid, his team is considering "whether there are additional things we can do to help Ukraine bolster its defenses in the face of Russian aggression."

Merkel and other European leaders staunchly oppose arming Ukraine, in part out of fear of sparking a proxy war with Russia.

The U.S. and Europe have largely been in agreement on their response to the conflict between Russia and Ukraine, raising the prospect that a public split over lethal aid is a tactic to push Russian Vladimir Putin to agree to a peace plan.

During a joint news conference with Obama, Merkel reaffirmed that she sees no military solution to the fighting in eastern Ukraine. However, she added that no matter what Obama decides, "the alliance between the United states and Europe will continue to stand, will continue to be solid."

Merkel and French President Francois Hollande met with Putin and Ukrainian leaders last week and announced a new summit meeting for Wednesday in Minsk. The United States was not at the negotiating table last week, nor will it participate in Wednesday's talks.

The European Union decided Monday to temporarily hold off on slapping more sanctions on Russians and Ukrainian separatists while awaiting the outcome of the peace talks.