Just one day after a peace deal was reached in Minsk new shelling has been reported around the rebel-held east Ukrainian cities of Donetsk and Luhansk.
There are no confirmed reports of casualties. Both cities are near the front line where the pro-Russian rebels face government forces.
The ceasefire agreed in Minsk, Belarus, is to begin in eastern Ukraine on February 15 at 00:00 local time.
The EU has warned Russia of additional sanctions if the deal is not respected.
On Friday morning, a military spokesman in Kiev said eight members of Ukraine’s military had been killed in fighting against separatists in the past 24 hours.
Meanwhile, rebels said seven civilians had been killed, reported AFP. Two people were also killed on Friday morning when rebels shelled a cafe in Shchastya, near Luhansk, said the head of the Kiev-controlled regional administration.
“So this is how a comprehensive ceasefire is prepared for,” said Hennadiy Moskal in a statement.
He was echoing wider doubts about the peace deal agreed following marathon negotiations between Russia, Ukraine, Germany and France.
Pro-Russian rebels have signed the agreement, which also includes weapon withdrawals and prisoner exchanges, but key issues remain to be settled.
A new round of EU asset freezes and travel bans against 19 Ukrainian separatists and Russians – in response to deadly fighting in the city of Mariupol in January – will come into effect on Monday regardless of the latest deal.
German Chancellor Angela Merkel says wider measures could be implemented if the ceasefire is not upheld.
She has called the deal “a glimmer of hope”, adding: “It is very important that words are followed by actions.”
Russia has reaffirmed it is playing no direct role in the conflict, with Kremlin spokesman Dmitry Peskov insisting it is only a “guarantor”:
“It is not a party that has to take action in this matter. We simply cannot do that physically, because Russia is not a participant in this conflict,” he said.
Ukrainian President Petro Poroshenko says the rival military commanders will hold direct talks – including on the withdrawal of heavy armor to create a buffer zone.
He warned that implementation of the agreement, reached by leaders in the Belarusian capital Minsk, would be difficult.
Another sticking point is the disputed town of Debaltseve, a strategically key government-held town which rebels claim to have surrounded but which Ukraine refuses to surrender.
Further talks will also be held on self-rule in parts of Donetsk and Luhansk separatist regions.
The truce is to be monitored by the Organization for Security and Co-operation in Europe (OSCE) – but with only 412 international monitors in Ukraine, including 226 in the Donetsk and Luhansk regions, some analysts have expressed doubt that they are there in adequate numbers to do the job.
Ukraine and the West accuse Russia of supplying weapons and personnel to the rebels but Russia denies this.