Igor Girkin claims to have touched off the conflagration, and he says he's proud of what he did. The former member of the Russian security service has a knack for turning up in tumultuous places.
The talks that began on Wednesday were expected to be continued today in Minsk. Belarus, which is hosting the dialogue, declined to comment on the reason.
In his annual Christmas Day blessing, the pontiff condemned killing in Iraq, Syria and Pakistan and the "brutal persecution" of religious and ethnic minorities.
The reaction comes after President Obama signed an executive order on Friday slapping economic sanctions on Crimea, a day after the EU approved similar measures.
The Boeing 777 that crashed over the area on July 17, killing nearly 289 aboard, is widely believed to have been downed by a Russian-built, rebel-operated surface-to-air missile battery.
President Obama and Canada's Prime Minister Stephen Harper were among those who gave the Russian leader an earful over Moscow's involvement in Ukraine.
The alleged movement continues to put into question a ceasefire that went into effect in September. It also comes after separatists held elections and Russia recognized them.