Seven Ukrainian soldiers were killed and seven wounded on Tuesday (local time) when their armoured column was ambushed by pro-Russian separatists near the eastern Ukrainian town of Kramatorsk, the defence ministry and state security service said.
It was the biggest single loss of life by the Ukrainian army since soldiers were sent into the mainly Russian-speaking east of the country to break up armed separatist groups who have seized control of towns and public buildings to push their demands for autonomy.
The ministry, in a statement published on its website, said an armoured column came under fire as it approached a bridge near a village 20 km from Kramatorsk, one of several hot spots in the region where the army has had only limited success against the separatists.
About 30 rebels, who had taken cover among bushes along a river, attacked with grenade-launchers and automatic weapons, immediately killing two soldiers and wounding three others, it said.
"In all, as a result of the prolonged fighting, six members of the armed forces were killed. Eight soldiers were wounded, one of them seriously," it said.
The state security service (SBU) said later that the seriously wounded soldier had died while being transported to hospital.
Before the Kramatorsk incident, Defence Minister Mikhailo Koval said a total of nine servicemen had been killed so far in the army's "anti-terrorist" operation, which has been directed mainly against rebels in the towns of Slaviansk and Mariupol.
The dead included five pilots, Koval said, who apparently died when their helicopters were downed by separatist fire.