Ukrainian government forces have no intention of renouncing a ceasefire in the separatist-held east of the country, a military spokesman said on Thursday.
But he reiterated that a buildup of forces in the regions the separatists control in eastern Ukraine signalled the pro-Russian rebels were planning a new offensive in a conflict that has killed more than 4,000 people.
The two-month-old truce has been violated daily, and increasingly in the past week. Each side has blamed the other for the violations.
"There is no intention of abandoning it (the ceasefire) despite all ... attempts to break these agreements by the Russian side," Ukrainian military spokesman Andriy Lysenko told a news briefing in the capital Kiev.
Kiev and the West say the separatists have received reinforcements of equipment and troops from Russia. Moscow denies accusations by NATO that it has sent in troops and tanks in the past few days and says it wants the ceasefire to work.
In remarks published on Thursday, Ukraine's representative to the OSCE security and rights body told a German newspaper it was now hardly possible to speak of a ceasefire, citing 2,400 alleged breaches of the truce by rebels.
Lysenko said shelling in residential areas of the separatist-held Luhansk and Donetsk regions had intensified and that there had been no let-up in the flow of equipment to rebels from Russia.
"We can't predict when (an attack could happen) but we must always be prepared," he said, adding that reserve army units were being prepared for action in case they were needed.
He said four Ukrainian servicemen had been killed in the past 24 hours.