Ukraine has promised to continue its offensive against pro-Russian militants despite the deadly loss of one of its helicopters.

At least 12 soldiers were killed when rebels shot down the craft on Thursday on the outskirts of Slovyansk.

The country’s acting defence minister, Mykhailo Koval, has again accused Russia of mounting a special military operation.

“Our troops have ousted separatists from southern and western parts of the Donetsk region and the north of the Luhansk region,” said Koval.

Meanwhile, it has emerged that another team of OSCE monitors has been detained in eastern Ukraine.

The group of four was stopped by armed men in the town of Severodonetsk, some 100 kilometres north of Luhansk.

Another team of election monitors was last heard from five days ago after being seized near Donetsk.