The European Union says the death of a Georgian man in the breakaway region of South Ossetia and the detention of two others is a "source of grave concern."

Maja Kocijancic, the spokesperson for EU foreign policy chief Federica Mogherini, said in a statement on February 25 that the EU is ready to support the investigation into the death of Archil Tatunashvili.

Authorities in the Russia-backed separatist region say 35-year-old Tatunashvili died of heart failure on February 22 while in custody. They say the incident followed an attempt by the man to attack police officers during his transfer to a detention cell after interrogations.

Georgian officials and Tatunashvili's relatives are demanding that the man's body be transferred to Tbilisi for an autopsy.

Separatist authorities say Tatunashvili was suspected of plotting terrorists acts in South Ossetia.

Two other Georgian men, Levan Kutashvili and Ioseb Pavliashvili, were detained together with Tatunashvili but later released from custody.

Kocijancic’s statement urged authorities in South Ossetia to allow them to travel to Tbilisi-administered territory.

“These latest developments underline the need for additional measures to ensure transparency and improve confidence” between the separatists and Tbilisi, it also said.

South Ossetia and another Georgian breakaway region, Abkhazia, have declared independence from Georgia.

Russia recognized the regions as independent states following a short war with Georgia in August 2008. Only a few countries followed Russia's lead in recognizing the entities' independence.

The EU statement reiterated that the bloc supports "the sovereignty and territorial integrity of Georgia within its internationally recognized borders.”

With reporting by civil.ge