Pro-Russian militants walk on the grounds of the Ukrainian National guard unit in the eastern Ukrainian city of Lugansk on May 29, 2014. Ukrainian forces suffered new 'losses' on May 28 during a rebel offensive in the eastern stronghold region of Lugansk, Kiev's volunteer National Guard defence force said in a statement. The volunteer National Guard said gunmen had sprung a surprise raid on May 28 on their barracks in the flashpoint Lugansk region near Russia that had been under effective rebel control since early April. AFP PHOTO/ ALEX INOY (Photo credit should read ALEX INOY/AFP/Getty Images)

VIENNA, May 30 (Reuters) - Another team of monitors of the Organization for Security and Cooperation in Europe has been detained in eastern Ukraine, the Vienna-based OSCE said on Friday.

The OSCE said the team of four international monitors and a Ukrainian language assistant was stopped in the town of Severodonetsk, 100 km (60 miles) north of Luhansk by armed men.

It said it had lost contact with the team at around 7 p.m. (1600 GMT) on Thursday.

The detained team from the OSCE's special monitoring mission is in addition to another team still missing in the east of the country, which was last heard from on the evening of May 26, the OSCE said.

A rebel leader had said on Thursday that team was likely to be released soon.

The OSCE has sent the so-called special monitors to observe compliance with an international accord for de-escalating a crisis in eastern Ukraine, where pro-Russian separatists have seized control of strategic points in several towns.

There are currently 248 international members of the OSCE's special monitoring mission in Ukraine, with another 23 due to be deployed on Friday and a target of 300 by the end of June, an OSCE spokesman said.

The OSCE - Europe's security watchdog, of which both Russia and Ukraine are members - also has teams of military observers in Ukraine led by the German Defense Ministry, and election observers who monitored last weekend's presidential vote.

(Reporting by Georgina Prodhan; Editing by Fredrik Dahl; Editing by Alison Williams)