The foreign ministers of Ukraine, Russia, Germany, and France have failed to agree on terms for a summit later this week aimed at defusing the crisis in eastern Ukraine.
German Foreign Minister Frank-Walter Steinmeier made the announcement after four hours of talks in Berlin on January 12 with Russian Foreign Minister Sergei Lavrov, French Foreign Minister Laurent Fabius and Ukrainian Foreign Minister Pavlo Klimkin.
He said the meeting had been a "very open exchange" but did not produce the results needed for the countries to go ahead with a meeting of leaders this week in Kazakhstan.
Steinmeier said representatives from their ministries would meet in the coming days to see if they could bridge differences.
"If there is progress made at that level in the coming days, then we are prepared to meet again next week and resume this discussion we began today," he told reporters.
In a joint statement, the four ministers also called on the contact group of Ukraine, Russia, and the Organization for Security and Cooperation in Europe (OSCE) to meet to try and make progress on implementing a much-violated Ukraine peace deal drawn up in September, including creating the "relevant conditions for an effective cease-fire."
If this is done, it would "pave the way to the preparation of a successful summit meeting" in Kazakhstan, they wrote.
The meeting followed a flurry of diplomacy, including a brief weekend encounter in Paris between the German, French, and Ukrainian leaders.
Speaking in Moscow on January 12, Russian Foreign Minister Sergei Lavrov said Russia expected the meeting in Berlin "to help stimulate a full implementation of everything agreed upon in Minsk by all parties."
Lavrov was referring to an often-violated deal on a cease-fire and steps toward peace agreed in Minsk on September 5.
German Chancellor Angela Merkel spoke by phone with Russian President Vladimir Putin on January 10 and met on January 9 with Kazakh President Nursultan Nazarbaev, the proposed host of a possible four-way summit on Ukraine.
Merkel told Putin that she expected Moscow to use its influence on pro-Russian separatists in eastern Ukraine to reach "consensual solutions."
She said a summit will not be held until progress has been made on the Minsk plan.
Russia denies playing any role in the conflict, despite evidence -- some provided by NATO -- that it has sent troops and weapons into Ukraine to support the separatists.
Speaking in Moscow on January 12 ahead of the meeting, Foreign Minister Sergei Lavrov said Russia expected the meeting in Berlin "to help stimulate a full implementation of everything agreed upon in Minsk by all parties."
At a news conference with Latvian Foreign Minister Edgars Rinkevics, whose country holds the rotating European Union presidency, Lavrov said that "the key point everyone agrees upon is that we ought to support the efforts to renew the territorial integrity of Ukraine."
But Lavrov said that the main sticking point remains Ukraine's lack of progress in implementing constitutional reform.
Lavrov once again criticized international sanctions against Russia over its role in the Ukrainian crisis, saying the sanctions are "absolutely illegitimate, counterproductive, and restrictive measures."
Rinkevics said "serious disagreements" over the conflict in Ukraine mean it may take a long time to find a solution.
The cease-fire agreed in Minsk is violated almost daily, and more than 4,700 people have been killed in fighting between government forces and pro-Russian separatists in eastern Ukraine since April.
On January 11, Merkel briefly met in Paris with French President Francois Hollande and Ukrainian President Petro Poroshenko.
Merkel and Poroshenko were among world leaders in the French capital to attend a rally to honor the victims of the recent terror attacks in Paris.
Hollande has said he would go to a Kazakhstan summit only on condition that there is a chance of making progress.
Russia also said the Kazakhstan summit might not take place.
On January 12, the daily Vedomosti quoted Putin's spokesman, Dmitry Peskov, as saying that "preparatory work continues...and our further actions depend on its outcomes."
Meanwhile, on the ground in eastern Ukraine, heavy fighting was reported in the pro-Russian separatist stronghold of Donetsk.
On January 12, Ukrainian military spokesman Andriy Lysenko said that "separatists" had attempted to storm Donetsk airport, which remains under the control of Ukrainian government forces.
Lysenko said the separatist assault was repelled.
The French AFP news agency reported that rocket and mortar fire echoed across Donetsk overnight on January 11-12 in what it described as some of the fiercest fighting there since the summer.
With reporting by dpa, AP, TASS, Reuters, AFP, and Vedomosti