Kiev: The Organisation for Security and Cooperation in Europe said on Friday it had lost contact with a second four-member international team in restive eastern Ukraine.
The Vienna-based security body said it had not heard from its team in the industrial region of Lugansk since Thursday evening when it was stopped "by armed men" at a roadblock in the town of Severodonetsk.
"The team was comprised of four international monitors and a Ukrainian translator," the OSCE`s Special Monitoring Mission for Ukraine said in a statement posted on Facebook.
"The team was travelling in two cars."
The organisation added that another four members who were detained by separatist rebels in the neighbouring Donetsk region on Monday were still missing.
The self-proclaimed "people`s mayor" of the Donetsk region rebel stronghold of Slavyansk confirmed on Thursday that the OSCE team that went missing on Monday was being held on suspicions of spying.
Another pro-Russian rebel from the little-known Southeastern Front claimed in a statement issued to the Interfax news agency earlier on Friday that his men had detained the team in Lugansk.
But a spokesman for the self-proclaimed "Lugansk People`s Republic" contacted by AFP denied that the group was being held against its will.
"Nobody arrested the four OSCE observers," Volodymyr Inogorodskiy told AFP.
"They finished their work late (Thursday) night in Severodonetsk and we advised them not to leave the city because of the (security) situation," said the spokesman.
The Special Monitoring Mission currently has 210 unarmed civilian members from European nations and 70 local staff who are supposed to facilitate dialogue between pro-Russian separatists and state authorities.
But their mission has been treated with suspicion by the rebels throughout their seven-week insurgency.
Seven OSCE monitors were branded "prisoners of war" and held in Slavyansk for eight days prior to their release under pressure from both the West and Russia on May 3. An eighth member of that group was set free due to ill-health after two days.
Another group of 11 OSCE observers was detained in the Donetsk province on Wednesday. The OSCE said it had managed to re-establish contact with them by the end of the night.
The latest disappearance of European monitors in the vital rust belt region underscores the trouble newly elected president Petro Poroshenko will have keeping his ex-Soviet republic intact.
Rebels in control of the Lugansk and Donetsk government buildings have declared independence and are seeking a merger with Russia similar to that accomplished by Ukraine`s Black Sea peninsula of Crimea following its seizure by pro-Kremlin troops in March.