Europe’s security watchdog said Friday it lost contact with another team of international monitors in eastern Ukraine.

The Organization for Security and Cooperation in Europe said the team of monitors was detained in Severodonetsk, about 60 miles from Luhansk in eastern Ukraine, the same area where another team is being held by rebels. That team hasn’t been heard from since Monday.

The OSCE said it lost contact with the second team early Friday morning, Reuters reported. Self-proclaimed Slovyansk “People’s Mayor” Vyacheslav Ponomarev told the Associated Press on Thursday that the first group of monitors would be released soon.

"I addressed the OSCE mission to warn them that their people should not over the coming week travel in areas under our control. And they decided to show up anyway," he said. “We will deal with this and then release them.”

The monitors are in Ukraine to observe whether an international agreement to de-escalate tensions in the eastern part of the country is being followed. Pro-Russian separatists have take control of various towns in the region.

An OSCE spokesman told Reuters that there are 248 international members of the organization in Ukraine and that another 23 monitors are expected to be in the country by Friday. The OSCE, of which Ukraine and Russia are a part, has a target of deploying 300 monitors by June.

The OSCE’s mission is being led by Germany’s defense ministry and election observers who monitored Sunday’s presidential election, which was won by billionaire businessman Petro Poroshenko.