The united resolve by President Barack Obama and British Prime Minister David Cameron comes ahead of the latter's two-day trip to Washington.
Ukrainian forces are losing ground inside Donetsk airport as rebel fighters impose themselves.
The delay may cost France billions in penalties if Russia proceeds with legal action.
Experts agree that the war in eastern Ukraine will get worse as a peace summit is canceled.
After months of fighting, pro-Russian forces are close to taking a key target in the Ukrainian civil war.
Russian, German and French leaders had been invited to talks in the Kazakh capital Astana by Ukrainian President Petro Poroshenko.
Almost a year after his downfall, Viktor Yanukovych is on the wanted list at the request of those who ousted him.
Several world leaders marched together, in Paris, in a show of solidarity against terrorism.
The foreign ministers of France, Germany, Russia and Ukraine will meet in Berlin on Monday to discuss the situation.
Cameron and Obama will discuss a number of issues at hand, like the situation in Ukraine, the Islamic State group and counterterrorism.
Russian Finance Minister Anton Siluanov says his country has legitimate grounds to demand immediate repayment of the debt.
State Department spokeswoman Jen Psaki said there were concerns about the health of the pilot, who is on a hunger strike.
According to Indonesian officials, divers are working to retrieve the crashed plane's tail from the Java Sea.
After nine months of fighting in eastern Ukraine, Russia may at last be ready to cooperate to save its shaky economy.
The IMF has cobbled together a $17 billion program for Ukraine but says $15 billion more is needed.
Three more Ukrainian soldiers died on the Eastern Orthodox Christmas Day, despite a ceasefire being in place.
Two German government websites were taken down for almost five hours on Wednesday in protest of a meeting with Ukrainian leadership.
The latest move will likely make it easier for Russian military forces to hire locals in regions beyond Russia's borders.
France's Hollande and Germany's Merkel want to meet with Ukrainian and Russian leaders, but they don't want to waste their time.
A Lithuanian military official says one detainee was embedded among his own officers.
The Obama administration tried to heal its relationship with Russia behind the scenes this year, according to a Bloomberg report.
Vladimir Putin celebrates 15 years in power on Wednesday. A lot has changed since he became president on New Year's Eve 1999.