A Serbian court on Friday ordered the continued detention of and investigation into the three Kosovo police officers who were arrested in Serbia earlier in the week.

The opening of legal proceedings came after the US special envoy for southeastern Europe, Gabriel Escobar, demanded the release of the officers, in line with the demand from the US State Department a day earlier.

"They either had been taken or ended up in Serbia without having intended it," Escobar said in an online press conference. "They should be released without conditions."

Serbia moves ahead with investigation

The Public Prosecutor's Office in the Serbian town of Kraljevo said it had charged the men with unauthorized production, possession, carrying and trafficking of weapons and explosive substances.

"The judge for the preliminary proceedings of the Higher Court in Kraljevo ordered the detention of all suspects," the prosecutor's office said in a statement.

The background of the initial arrest has been disputed by Serbia — which says the officers were deep inside Serbian territory — and Kosovo — which says the men were kidnapped.

Kosovo Prime Minister Albin Kurti welcomed the call for the police officers' release and repeated the Kosovar side of the story: "Serbia kidnapped them, on a road in Kosovo used by Serbian smugglers."

Fears of return to open conflict

The arrest of the Kosovar police officers is only the most recent episode in an ongoing escalation of tension between the two neighbors.

Members of the Serbian minority in northern Kosovo have been protesting against the election of ethnic Albanian mayors in their towns after the majority of ethnic Serbs boycotted the vote.

The protests broke out into violence which saw the Kosovo Serbs face off against Kosovo police and NATO-led peacekeepers, several of whom were injured in the clashes.

Serbia then ordered its troops to be deployed to the border and to be on highest alert. The EU, UK, and US have all called on both sides to de-escalate.

Serbia does not recognize Kosovo's independence which it declared in 2008 following a war in the late 1990s that left over 10,000 people dead, most of whom were from Kosovo's majority ethnic Albanian community.

ab/wd (Reuters, AP, dpa)