German Chancellor Angela Merkel is set to argue against arming Ukraine in its conflict against rebels in Washington on Monday in the face of intense US Congressional pressure.

Merkel's message that sending Western weapons to Kiev risks escalating the conflict is likely to get a sympathetic hearing when she meets US President Barack Obama later in the day.

But critics of Obama's cautious foreign policy approach are already demanding decisive US action to help Kiev fight the separatists in eastern Ukraine, even if this deepens a standoff with Russian President Vladimir Putin.

Nine Ukrainian troops have been killed in the past 24 hours and seven civilians also died, Kiev said on Monday.

At a security conference in Munich over the weekend, Merkel said it was uncertain whether further negotiations would lead to a deal with Putin but argued that all opportunities for a diplomatic solution should be pursued.

Merkel, who with French President Francois Hollande is due to meet Putin on Wednesday, has come under fire from US foreign policy hawks in the Republican-controlled Congress who want defensive weapons sent to Ukraine.

Merkel made clear her opposition to arming Kiev. "I understand the debate but I believe that more weapons will not lead to the progress Ukraine needs. I really doubt that," she said.

Last week, Merkel and Hollande met Putin in Moscow and followed this up with a conference call on Sunday that also included Ukrainian President Petro Poroshenko. The four are due to meet in Minsk on Wednesday, although German Foreign Minister Frank-Walter Steinmeier said Monday that it was not certain that the four-way talk will go ahead, with much work still to be done.

The Ukrainian government said after the phone call that the four leaders expected their efforts to lead to "an immediate and unconditional bilateral cease-fire."

Obama has to decide whether to supply weapons, impose tougher sanctions on Russia in the hope of forcing Putin to compromise, or throw his full weight behind the revised German-French peace initiative.

Moscow warned on Monday that Putin will not be spoken to in the language of ultimatums. Asked about media speculation Merkel had issued him an ultimatum at talks on arranging a summit on Ukraine, Kremlin spokesman Dmitry Peskov told Govorit Moskva radio that "Nobody has ever talked to the president in the tone of an ultimatum - and could not do so even if they wanted to."

EU foreign ministers approved on Monday enacting visa bans and asset freezes on more Ukrainian separatists and Russians but will wait until February 16 to implement the measures to give peace efforts more time, French Foreign Minister Laurent Fabius said.