Ukraine's military and Russia-backed rebels carried out a prisoner exchange Thursday in eastern Ukraine, a result of an agreement this week by the two sides to halt the ongoing violence by September 1.
Officials from both sides said 12 rebel prisoners were swapped for about the same number of Ukrainian servicemen.
A police spokesman for the self-proclaimed Donetsk People's Republic, Victor Anosov, said the exchange was the first one that took place in an atmosphere of trust.
Separately, Ukraine accused the rebels of multiple cease-fire violations.
The headquarters of Kyiv's "anti-terrorist operation" reported that separatist forces in eastern Ukraine violated the cease-fire 54 times Thursday. It said 11 of the violations involved artillery fire and 16 involved attacks using grenade launchers.
The ATO headquarters said the most intense fighting took place around the government-controlled port city of Mariupol.
Earlier Thursday, a spokesman for Ukraine's presidential administration on military issues, Oleksandr Motuzyanyk, said seven servicemen had been killed and 13 wounded in fighting over the previous 24 hours.
On Wednesday, representatives of Ukraine's government and the separatists meeting in Minsk under the auspices of the Organization for Security and Cooperation in Europe agreed to try to ensure that all fighting in eastern Ukraine ends by September 1, the start of the new school year.
Sporadic clashes have continued since the two sides agreed to a cease-fire in February, and the violence has escalated in recent weeks.
Russia seized Ukraine's Crimean Peninsula last year, after popular protests led to Kremlin-backed President Viktor Yanukovych's replacement by Western-leaning leaders. Yanukovych fled to Russia and the Kremlin began supporting rebels in Ukraine's east, although it has denied mounting evidence of military support.
Western governments hit Russia with economic and diplomatic sanctions after it annexed Crimea.