Obama, at a White House news conference with visiting German Chancellor Angela Merkel, said providing weapons to Ukraine was among the options he and his advisors were considering.

But he made clear he had reservations about upping the ante in Ukraine
and endangering U.S.-European unity in the contest of wills with Russian
President Vladimir Putin. Merkel opposes sending weapons to Kiev to
help it fight Russian-backed separatists.

"It
is true that if, in fact, diplomacy fails, what I've asked my team to
do is to look at all options," Obama said. "But I have not made a
decision about that yet."

Despite
prompting by a German reporter, the U.S. president pointedly declined
to lay down a 'red line' that, should Putin cross it, would prompt him
to authorize weapons for Ukraine.

In the face of a new offensive by separatists in eastern Ukraine,
some of Obama's top advisors, as well as hawkish U.S. lawmakers, are
pressing him to do more to help the Ukrainian government defend itself.

But
that question has been overshadowed, at least temporarily, by a revived
diplomatic push led by Merkel and French President Francois Hollande.
The two are due to meet with Putin and Ukrainian President Petro
Poroshenko in Belarus on Wednesday.

Obama has long been skeptical of arming proxies in places such as Syria and Ukraine, and "has not said anything ... to suggest he's moved on this issue," said Andrew Kuchins, director of the Russia and Eurasia program at the Washington-based Center for Strategic and International Studies.

But
Kuchins said that if the latest diplomatic effort fails, "then it will
be incumbent on the administration to do something in response," such as
increasing sanctions on Russia or considering arming Ukraine.

KREMLIN REJECTS ULTIMATUM TALK

The United States and the European Union say Russia has violated a September peace deal by sending more tanks and artillery into eastern Ukraine.

European Union ministers held off tightening sanctions on Monday to give the latest talks a chance.

Obama
said he and Merkel had agreed sanctions must stay for now and Moscow's
isolation would worsen if it continued on its current course.

With the previous peace deal having failed, Merkel made it clear she was not predicting success for the latest talks.

"I
myself actually would not be able to live with not having made this
attempt," she said. "There is anything but an assured success in all of
this. I have to be very clear about this."

Last
week, Merkel and Hollande met Putin in Moscow and followed this up with
a conference call on Sunday also including Poroshenko. But so far no
breakthrough has emerged in the nearly year-long conflict that has
claimed over 5,000 lives.

Nine Ukrainian troops were killed in a 24-hour period over Sunday and
seven civilians also died, Kiev said on Monday, with fighting
particularly intense around the town of Debaltseve, a major rail and
road junction northeast of the city of Donetsk.