HORLIVKA, Ukraine (Reuters) - Ukraine and pro-Russian separatist rebels conducted the largest exchange of prisoners since conflict broke out in 2014, sending hundreds of captives home to their families on Wednesday ahead of New Year and Orthodox Christmas.

More than 10,000 people have been killed in the conflict and casualties are still reported almost daily despite a ceasefire that froze the frontlines in place since 2015.

“My son rang,” the mother of a Ukrainian prisoner Oleksandr Oliynyk told the Ukrainian news channel 112.

“I have not heard his voice for three-and-a-half years, just letters. He said: ‘Mum, I’m already here.’ You cannot imagine what it means for a mother, to not see your child for three-and-a-half years, since August 2014.”

According to the terms of the deal, Kiev was meant to hand over 306 prisoners to the rebels and receive 74 prisoners in return. A Reuters photographer at the scene saw the Ukrainian prisoners being loaded onto buses in the town of Horlivka and taken to territory controlled by the Ukrainian government.

“All 74 Ukrainian hostages are already at home, on the territory controlled by our army,” Ukrainian President Petro Poroshenko wrote on social media.

According to Poroshenko, among the prisoners handed to Ukraine were a historian and a “cyborg” - the nickname Ukrainians gave to soldiers who defended Donetsk airport in one of the conflict’s most intense battles in 2014.

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The exact number of prisoners exchanged is uncertain. Viktor Medvedchuk, Ukraine’s representative to ongoing peace talks, said some captives held by Ukraine refused to return to rebel-held areas, according to the Russian news agency TASS.

More prisoners are expected to change hands in 2018, TASS cited Medvedchuk as saying. The Ukrainian state security service said 103 prisoners remained in separatist hands.

There was no immediate comment from the authorities in Moscow, which Ukraine and its Western allies accuse of supporting the pro-Russian separatists with troops, cash and heavy weapons, an accusation Moscow denies.

German Chancellor Angela Merkel and French President Emmanuel Macron welcomes the exchange in a joint statement and called on both sides to release the remaining captives.

Germany’s foreign ministry said it was a significant step in implementing the ceasefire agreement agreed in the Belarus capital Minsk.

“Above all, it is also an important humanitarian gesture before the New Year and Orthodox Christmas,” a foreign ministry statement said.

The Minsk agreements, intended to end the fighting in Ukraine, were signed by Ukraine, Russia, Germany and France in the Belarussian capital in early 2015.

The exchange came as U.S. Secretary of State Rex Tillerson asked Russia to “lower the level of violence” in eastern Ukraine.