KIEV: Kiev and pro-Russian separatists will exchange hundreds of prisoners soon, an aide to the head of Ukraine’s SBU state security service said on Friday, as the military reported a slight increase in rebel attacks.

The agreement to swap 125 Ukrainian servicemen for 225 rebels held by Kiev followed peace talks between envoys of Ukraine, Russia, the separatists and European security watchdog OSCE on Wednesday.

“We’ve prepared 225 people, which we will hand over. The main thing is for this not to fall through now,” the SBU’s Markiyan Lubkyvsky told Reuters by telephone.

The uprising by separatists began a month after Russia annexed the Black Sea peninsula of Crimea from Ukraine in March, following the popular overthrow of Ukraine’s Moscow-backed president, and has killed more than 4,700 people.

The pro-Western government in Kiev accuses Russia of orchestrating the rebellion in Ukraine’s east, a charge denied by Moscow.

Exchanging prisoners is one of the criteria of a 12-point peace protocol, which also includes a cease-fire, agreed by Kiev and rebels in September. But most of the plan has not yet been implemented due to repeated violations of the cease-fire and because separatists defied Kiev by holding leadership elections.

Ukraine’s Interfax news agency quoted a rebel representative as saying the prisoners would be swapped by Dec. 30. Lubkyvsky did not confirm this date, but said the exchange would happen “soon.”

It is not known exactly how many prisoners are currently held by the two sides, but Ukraine’s military said this month around 600 Ukrainians were in rebel hands.

Around 1,300 people have been killed since the cease-fire was agreed in September, according to the United Nations, but the fighting has lessened significantly in December.

On Friday, however, the military said rebels had slightly stepped up their attacks on Ukrainian positions in the east of the country.

“In the past two days, (rebel) fighters started using artillery and GRAD rocket launchers. Attacks have intensified to a minor extent,” military spokesman Andriy Lysenko told Reuters by phone.

Meanwhile, Ukraine’s state rail company Ukrzaliznytsia said on Friday it would suspend passenger and cargo train services to the Black Sea peninsula of Crimea, which was annexed by Russia in March, due to security concerns.

Ukrzaliznytsia said cargo trains would be suspended from Friday, while passenger routes would gradually cease running over the weekend and on Monday. It did not say how long the suspensions would be in place or specify what the security concerns were.

“In order to ensure the safety of passengers ... (the railway) will cut the route of trains to Crimea off at Novooleksiyvka and Kherson,” it said in a statement, referring to two towns on the Ukrainian mainland near Crimea.

Russia annexation of Crimea pushed relations between Moscow and the West to their lowest point since the Cold War, and a month later a separatist uprising began in eastern Ukraine.