Dutch captain Evert-Jan Daniels confirmed that two infected Dutch soldiers were flown to the Netherlands for treatment but declined to disclose the nationalities of the other affected troops.

"At this moment there are in total 20 cases," he said, without elaborating

NATO deployed four multinational battalions of about 1,000 troops in Lithuania, Latvia, Estonia and Poland three years ago to beef up defences on the eastern flank after Russia's 2014 annexation for the Crimea region from Ukraine.

In a statement, the battalion said it was carrying on its mission while "conducting reduced trainings" in order to maintain its readiness.