Ukrainian forces have rejected a proposal from pro-Russian rebels to create a safe corridor for troops to leave the encircled town of Debaltseve in eastern Ukraine.
Separatists had offered to allow troops leave the town, which is the focus of heavy fighting despite a ceasefire deal, if they lay down their arms.
Military spokesman Vladislav Seleznyov said the town lies within territory under Ukrainian control in accordance with a ceasefire deal reached in Minsk last week.
"There are the Minsk agreements, according to which Debaltseve is ours. We will not leave," he said by phone.
The Ukrainian government says pro-Russian separatists are continuing to shell the strategic railway junction, despite a ceasefire coming into effect at midnight yesterday.
"The illegal armed groups are not supporting the ceasefire," military spokesman Anatoly Stelmakh told reporters.
Mr Stelmakh said the number of attacks on the town have increased in comparison to recent days.
He added the Russian-backed rebels were using Grad rockets and tanks to attack government forces holding the town.
Mr Stelmakh said government forces had only fired when coming under attack.
Another military spokesperson has said there is no question of Ukraine withdrawing heavy weapons from the frontline due to continuing attacks by pro-Russian rebels.
Vladyslav Seleznyov said: "How can we pull back weapons if the rebels are trying to attack us with tanks, and are constantly firing at us?"
A military spokesperson said five Ukrainian soldiers have been killed in attacks in separatists since the ceasefire came into effect.
Meanwhile, the European Union has also published a new list of Ukrainians and Russians placed under sanctions including travel bans and asset freezes.
The list includes two Russian deputy defence ministers, along with three other Russians, 14 Ukrainians and nine entities.
Russia's foreign ministry has criticised the sanctions, saying that they contradict common sense and will not help to find a solution to the conflict in Ukraine.
In a statement it also said it will "adequately" respond to the sanctions.
