European security watchdog OSCE said on Tuesday it had lost contact with one of its teams of monitors near the city of Donetsk in eastern Ukraine, where pro-Russian militants are clashing with Kiev government forces, Reuters reported.

The four-strong international team was on a routine patrol east of Donetsk when contact was lost around 6 pm (1500 GMT) on Monday, May 26 evening, the Organization for Security and Cooperation in Europe said in a statement.

"We have been unable to re-establish communication until now," it said. "We are continuing with our efforts and utilizing our contacts on the ground. The Ukrainian government as well as regional authorities have been informed of the situation."

In early May, pro-Russian activists in Ukraine's east freed seven European military observers from a separate OSCE-linked mission after holding them hostage for eight days.

The 57-nation OSCE - which seeks to prevent conflict and promote democracy on the continent - decided unanimously in March to deploy civilian monitors across Ukraine to try to help defuse the crisis there, so far without much success.

The mission consists of about 282 people, including 198 civilian international monitors from 41 OSCE countries, according to the Vienna-based organization’s website.