The United States on Sunday called on all sides in the Ukraine conflict to refrain from any actions that undercut current peace efforts and voiced concern about renewed "fierce fighting".
"We call on all parties to refrain from actions that undercut the current diplomacy," said State Department spokeswoman Jen Psaki, who was travelling with Secretary of State John Kerry in Germany.
"We continue to support the ongoing diplomatic efforts by our European colleagues and remain in lockstep that any agreement must respect the sovereignty and territorial integrity of Ukraine," she said.
The French, German and Ukrainian leaders are planning with Russian President Vladimir Putin to meet Wednesday in an urgent bid to hammer out a peace deal.
The four spoke by phone on Sunday as part of efforts to achieve a "comprehensive settlement" to end 10 months of fighting between Ukrainian forces and pro-Russian rebels in the east which has cost some 5,400 lives.
"Secretary Kerry will remain closely engaged, as he has over the course of the last few days in Ukraine and Munich, as the discussions continue," Psaki said, referring to Kerry's visits to Kiev and the Munich Security Conference in Germany.
Psaki said the United States remained "concerned about the fierce fighting today in Debaltseve and Mariupol, and press references to new Russian convoys into eastern Ukraine.