Paris (France) (AFP) - French President Francois Hollande and German Chancellor Angela Merkel lamented the "insufficient" progress in resolving the Ukraine crisis after a telephone conversation Monday with Russian President Vladimir Putin, according to a source close to the French president.

"The chancellor and the president (Hollande) raised the need to put pressure on the various parties" given that progress is "insufficient," the source said, a day before foreign ministers from Ukraine, Russia, France and Germany hold talks in Paris on the crisis.

The three-way call, which lasted 45 minutes, came after EU foreign ministers formally agreed to prolong damaging economic sanctions against Russia until January 2016, in order to pressure Moscow to fully implement a February peace deal.

In addition, NATO head Jens Stoltenberg said earlier Monday the alliance would approve plans this week to more than double the size of its rapid response force, having already created a special spearhead unit as part of the fallout from the Ukraine crisis.

The 15-month-long conflict in Ukraine has claimed the lives of nearly 6,500 people and driven more than a million from their homes.

Ukraine and the West accuse Russia of sending regular troops into eastern Ukraine to boost separatist forces in the Donetsk and Lugansk regions -- accusations Moscow flatly denies.

A ceasefire agreement agreed in February in the Belarus capital Minsk has proven extremely shaky, with sporadic clashes continuing in parts of the conflict zone.