Kiev - Ukraine's army and separatist rebels on Sunday appeared to be complying at least partially with their truce accord, saying they will start pulling back heavy weapons from the frontline after carrying out a prisoner exchange.
But ongoing breaches of a week-old ceasefire - especially by the pro-Russian rebels, who overran a strategic town in a bloody offensive - have already prompted a threat from the United States of "serious" new sanctions against Moscow within days.
A journalist in the eastern rebel stronghold of Donetsk heard intense shelling for an hour early on Sunday to the north of the city, near the regional airport that fell to the rebels a month ago after fierce battles.
Fears were also rising over Mariupol, a government-held port city that is rapidly becoming another flashpoint. Continued shelling has been reported there and Kiev alleges that 20 Russian tanks have been deployed towards it.
Despite those hostilities, Ukrainian officials and the separatists said they have jointly agreed to finally start the pullback of heavy weapons - a step meant to have begun on Tuesday and completed by 3 March under the truce.
The offensive killed 179 soldiers over the past month, according to one Ukrainian presidential aide. Some 2 500 Ukrainian troops had to flee Debaltseve under heavy rebel fire.
Also read: Ukraine troops taken prisoner in railway hub fighting
The Debaltseve rout and other ceasefire breaches have drawn a furious reaction from the United States, which blames Russia for the 10-month conflict despite Moscow's repeated denials.
"If this failure continues, make no mistake, there will be further consequences including consequences that will place added strains on Russia's already troubled economy," US Secretary of State John Kerry stormed during a press conference in London on Saturday.
He believed President Barack Obama would "in the next few days" decide on "additional steps (that) will be taken in response to the breach of this ceasefire". He predicted "serious sanctions" could be imposed.
The United States and the European Union have already imposed several rounds of sanctions on Russia.