NIZHNYAYA KRYNKA, Ukraine — Pro-Moscow rebels said they would start to withdraw heavy weapons from the front line in eastern Ukraine on Sunday but the government in Kiev said armored columns had crossed the border from Russia to reinforce the separatists.
The Ukrainian military said the rebels were pressing on with attacks on government forces near Mariupol, a port in government hands that is seen as the rebels' next major target.
Spokesman Andriy Lysenko said a military train carrying 60 armored vehicles including tanks had arrived in the town of Amvrosiivka from Russia on Saturday. A convoy of military equipment had later crossed the border near Novoazovsk, east of Mariupol on the Sea of Azov.
He said fighting was in progress at the village of Shyrokyne, east of Mariupol.
"The fight continues. Our soldiers are holding their positions," Lysenko said, adding that there had been a total of 44 attacks by separatists across the conflict zone in the past 24 hours.
A pro-Russian rebel commander said the separatists were due to begin pulling back heavy weapons from the frontline in eastern Ukraine on Sunday, a sign that the rebels may be prepared to halt their advance as part of an internationally brokered peace deal.
Fighting has eased in many areas since a ceasefire came into effect a week ago, but the truce was shaken by the rebel capture on Wednesday of the town of Debaltseve, forcing thousands of Ukrainian troops to retreat.
Meanwhile, in the city of Kharkiv, three people were killed and 10 wounded on Sunday when an explosive device was thrown from a car into a crowd attending a peace rally, a Ukrainian regional prosecutor said.
The blast, which police called a terrorist act, occurred near a metro station as a crowd of participants in the rally passed by.
On Saturday, government forces and rebels exchanged nearly 200 prisoners, one of the first moves to implement the peace deal reached on Feb. 12 in the Belarussian capital Minsk after the French, German, Russian and Ukrainian leaders met.