On Sunday, hours after the eight military observers from the Organization for Security and Co-operation in Europe (OSCE) spoke during a press conference held by their captors in Slovyansk, a Swedish member of the team was released (pictured above, center).

Pro-Russian separatists who have claimed control of Slovyansk escorted the man to a car belonging to the OSCE outside the city administration building where the group is being held. The car then drove away.

The Reuters news agency quoted a spokeswoman for the self-declared separatist mayor of Slovyansk as saying that the man had a mild form of diabetes and was released for that reason.

During the press conference earlier in the day, German Colonel Axel Schneider spoke to reporters on behalf of the OSCE group and said no one had been harmed, but they were not allowed to leave of their own free will.

"We have no indication when we will be sent home to our countries," he said.

Vyacheslav Ponomaryov, who has assumed control of Slovyansk as mayor, said he believed the group's release could be negotiated, but that they were being treated as NATO spies. The leader of the self-declared Donetsk Republic, Denis Pushilin, said on Saturday that OSCE group would only be released on the condition that an exchange take place for rebel prisoners being held.

Russia has 'not lifted a finger'

While speaking to reporters on Sunday, US President Barack Obama hit back at Russia's calls for a de-escalation of tensions in Ukraine, accusing the country of aggravating the situation.

Moscow has "not lifted a finger" to deter rebels from their actions in Ukraine, Obama said a press conference in Kuala Lumpur, where he had been meeting with the Malaysian prime minister on the third leg of his Asia tour.

"In fact, there's strong evidence that [Russia has been] encouraging the activities in eastern and southern Ukraine," Obama added.

This week, Russia deployed thousands of troops to its southwestern border with Ukraine to conduct military exercises. The move has been viewed by the international community as a potential precursor to staging a military intervention that could see the annexation of more Ukrainian territory. The Crimea peninsula was annexed by Russia in March.

The US and EU plan to unveil further sanctions against Russian allies of President Vladimir Putin as early as Monday unless the country changes course. The decision follows a stronger set of restrictions placed on Russia by the leaders of the Group of Seven major economies on Saturday.

mz,kms/mkg (AFP, Reuters, dpa)