A group of Serbian war veterans who call themselves Chetniks have claimed to have killed 23 Ukrainian soldiers, on Russian Facebook equivalent VKontakte.

"Today our squad Jovan Shevich killed 23 soldiers of the Ukrainian criminal army and knocked out a significant number of armoured vehicles," read a message by the Chetniks' commander Bratislav Zivkovic on a pro-Russian rebel page, which carries the profile picture of separatist leader Igor 'Strelkov' Girkin. "Serbs do not spare their enemies. Enemies of the Russian world are enemies of the Serbs."

Strelkov, one of the most powerful commanders in eastern Ukraine, recently quit his post of minister of defence in the self-proclaimed Donetsk People's Republic (DNR).

Chetniks first emerged at the beginning of the last century as a nationalist and monarchist paramilitary group that fought in the Balkan wars and World War I. During World War II the name Chetnik came to identify a disparate number of militia groups that fought against Nazi Germans, Croats, rival communist partisan groups and Muslims, with the broad aim to secure an ethnically-pure Greater Serbia.

The group resurfaced as ethnic violence erupted during the Yugoslav wars in the 1990s. Zivkovic claimed he fought in Kosovo, Bosnia and Croatia.

The group's claims could not be independently verified.

The development came as Russia said that a group of Russian paratroopers who were captured by Ukrainian forces in eastern Ukraine had crossed the border "by accident".

Ukraine confirmed that 10 Russian paratroopers had been captured and, as proof of this, released interview footage with some of the captive military personnel. The country's security service said that the Ukrainian military had caught them near Dzerkalne village, 50km (30 miles) southeast of Donetsk, the Ukrainian city held by pro-Russian separatists.

The capture of the troops comes after Ukrainian president Petro Poroshenko announced he is dissolving parliament to prepare for elections in October, before he and Russian president Vladimir Putin meet at a summit in the Belarussian capital of Minsk. The summit, organised to discuss the ongoing crisis, is also set to be attended by senior European Union officials. It will mark the first face-to-face meeting of the pair since a World War Two commemoration ceremony in June.