Ukrainian authorities are accusing Russian-backed separatists of moving tanks, weapons, and fighters closer to the line of contact with government forces in the east of the country.
In a statement issued on March 23, Interior Ministry adviser Zoryan Shkiryak said that 10 to 12 tanks had arrived overnight in Horlivka, a rebel-held city close to the front line.
Shkiryak said that "the enemy continues to concentrate its forces in occupied areas of Donetsk and Luhansk," a reference to two provinces held in part by the separatists.
The Ukranian military, meanwhile, said that six government soldiers were wounded in the previous 24 hours despite a cease-fire deal signed in Minsk last month.
More than 6,000 people have been killed in the conflict in eastern Ukraine since April 2014.
Fighting has lessened since the cease-fire took effect on February 15, but fighting persists and the prospects for a resolution of the conflict are clouded by disputes over other aspects of the peace deal.
With reporting by Unian