According to the OSCE, the men are in good condition, but a second group, captured four days later, are still held captive.
Andrei Purgin, the first deputy prime minister of the self-proclaimed Donetsk People's Republic, told Interfax on Wednesday that militiamen, in the Donetsk region may release them within days, but news of the mens' imminent release had been reported weeks ago as well.
According to Delfi, the Estonian observer, named now as Tõnis Asson, was a high-level NATO official and a Lieutenant Colonel in the Estonian Defense Forces.
Asson was the Estonian Defense Forces' representative at NATO headquarters as late as 2012, but had been teaching after that.
The news website said Asson's past is one reason Estonian, Ukrainian and OSCE officials remained tight-lipped on the details of the captives.