Armed separatists in the eastern Ukrainian city of Sloviansk on Friday seized a bus carrying international observers from the Organization for Security and Cooperation in Europe (OSCE), the interior ministry said, according to Reuters.
The group, which included 7 OSCE representatives and five members of the Ukrainian armed forces, was being held in the building of the state security agency (SBU) in the city which has been occupied by pro-Russian separatists.
"Negotiations are going on for their release," a ministry statement said.
Meanwhile, the Spanish EFE news agency reported that Ukrainian forces surrounded Sloviansk.
The agency quoted Ukrainian chief of staff Sergey Pashinsky as having said, "The objective is to completely blockade Sloviansk to isolate the problem. The operation is being carried out at this time.”
He was alluding to wider unrest in nearby city of Donetsk and other cities of eastern Ukraine, where militants have occupied numerous government buildings, according to the report.
For his part, the commander of the operation in Sloviansk, Gen. Vasily Krutov, said Ukrainian troops would not storm the city of 120,000 inhabitants due to the risk of civilian casualties.
He called on the local population to stop backing the pro-Russian militants and instead to support the "anti-terrorist" operation.
Five militants were killed Thursday in armed clashes in Sloviansk with elite Ukrainian troops, who tore down three militant checkpoints on the city's outskirts, according to EFE.
Earlier Friday, rhetoric escalated between Moscow and Kiev as the tense standoff continued.
"Attempts at military conflict in Ukraine will lead to a military conflict in Europe," Acting Ukrainian Prime Minister Artseniy Yatsenyuk told the interim cabinet, in remarks on a live broadcast.
"The world has not yet forgotten World War Two, but Russia already wants to start World War Three."
Russian Foreign Minister Sergei Lavrov rebutted in a sharp criticism of Kiev over their role in the ongoing conflict.
"They (Kiev) are waging a war on their own people. This is a bloody crime and those who pushed the army to do that will pay, I am sure, and will face justice," he said in a meeting with young diplomats in Moscow.
The U.S. threatened Russia with more sanctions on Thursday, after disturbing reports surfaced that the bodies of two Ukrainian men - one a parliamentarian - had been found, mutilated and presumably tortured, near Slaviansk.
Eastern Ukraine in particular has been the seat of pro-Russian tensions since earlier this month, when neighboring Crimea held a controversial referendum vote and was annexed by Moscow after a de facto military invasion of the region.
(Arutz Sheva’s North American Desk is keeping you updated until the start of Shabbat in New York. The time posted automatically on all Arutz Sheva articles, however, is Israeli time.)