'Substantial and constructive' Ukraine talks

The phone call, planned for Sunday, will also include German Chancellor Angela Merkel and French President Francois Hollande. The German and French leaders left Moscow on Friday night following more than four hours of talks with Russian President Vladimir Putin.

Despite failing to reach an agreement to resolve the crisis in Ukraine, a French presidential source said on Friday that the talks had been "substantial and constructive," adding that leaders were working on a joint text incorporating proposals from both Putin and Poroshenko.

Merkel's spokesman Steffen Seibert also confirmed that "on the basis of a proposal by Germany's chancellor and France's president, a possible joint document to implement the Minsk agreement will now be worked on."

'No military solution'

The visit to Moscow on Friday came at short notice to Merkel, who traveled to the Russian capital for the first time since the Ukraine crisis began almost a year ago.

Speaking in Berlin, ahead of the talks with Hollande and Putin, Merkel said she was "convinced that there is no military solution to this conflict."

After September's truce was used by pro-Russian separatists to regroup and rearm, enabling them to seize more ground, top NATO commander Philip Breedlove warned on Friday that any ceasefire must be monitored by a group like the Organization for Security and Cooperation in Europe (OSCE).

At the Munich Security Conference, German Defense Minister Ursula von der Leyen also cautioned that arming Ukraine - something Ukrainian officials have repeatedly asked for - could backfire.

"The support with arms from Russia to the separatists is potentially unlimited. Do we really count on being able to provide as many arms to the Ukrainian army that they could potentially conquer the other side?" von der Leyen asked the conference.

New sanctions on Russia

European leaders are due to reconvene next week to discuss imposing new economic sanctions on Russia. The West and Kyiv have accused Moscow of sending troops as well as sophisticated weapons across the border to bolster separatists in Ukraine, despite the Kremlin's continued denial of playing any direct role in the ongoing conflict.

Speaking in Brussels on Friday, US Vice President Joe Biden called on the US and Europe to stand with Ukraine, which he said was battling for survival in the face of escalating Russian military involvement.

"Russia cannot be allowed to redraw the map of Europe. President Putin continues to call for new peace plans as his troops roll through the Ukrainian countryside, and he absolutely ignores every agreement his country has signed in the past," Biden said.

According to the United Nations almost 5,400 people have been killed in the conflict in the Donbass region of Ukraine since the annexation of Crimea by Russia in March last year.

ksb/bw (AFP, AP, Reuters)