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 kilometers north of Luhansk by armed men.
It said it had lost contact with the team at around 7 p.m. 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.