Ukraine has said it cannot start pulling heavy weapons from the front line due to rebels shelling its positions.
The Ukrainian military and the pro-Russian separatists had agreed to start withdrawing heavy weapons in eastern Ukraine this weekend.
Both the rebels and the Ukrainian military have two weeks to begin pulling back heavy weapons, under the terms of the Minsk peace plan agreed earlier this month.
If implemented, the deal would create a buffer zone of at least 140km for the heaviest types of weapons being used in the conflict.
But the peace deal has been violated numerous times since it was brokered by European leaders, along with the Russian and Ukrainian presidents, 10 days ago.
Two people were killed and around a dozen were injured when a bomb exploded in the east Ukrainian city of Kharkiv on Sunday (22 February).
The attack on the government-held city was being treated as a terrorist act, according to Ukraine's interior ministry.
The blast occurred at a march to commemorate the anniversary of the ousting of former president Viktor Yanukovych, who fled to Russia in 2014 amid massive popular protests.
Ukraine's security service said that four arrests had been made, and that the suspects had received training and weapons on Russian soil.
More than 5,600 people have been killed in eastern Ukraine since the conflict erupted in April 2014, according to UN figures.