Serbian troops have been put on full alert after heavily armed Kosovo police arrested 23 people in Serb-dominated northern Kosovo.

Police fired tear gas as they carried out the operation and several people on both sides were injured in the clash on Tuesday, and a Russian UN official was also detained.

The raid has raised tensions between Serbia and its former province, which declared independence from Belgrade in 2008 after a bloody 1998-1999 war that ended only after Nato intervened.

Serbs make up 90 per cent of the population in northern Kosovo and want to remain part of Serbia, not an independent Kosovo. Action by Kosovo special police there is rare and always triggers Serb anger.

In a sign of lingering tensions, Serb troops and armoured vehicles were seen leaving their barracks in central Serbia and headed towards the Kosovo border. An air force MiG-29 fighter jet made a low pass near the border with Kosovo, according to the state Tanjug news agency.

Kosovo: Remembering the war, 20 years on Show all 9 1 /9 Kosovo: Remembering the war, 20 years on Kosovo: Remembering the war, 20 years on A woman walks past pictures of victims displayed on a wall at the cemetery in Krusha e Madhe, Kosovo, on March 26, 2019, as part of commemorations marking the 20th anniversary of the Krusha e Madhe massacre. AFP/Getty Kosovo: Remembering the war, 20 years on Kosovo Albanian children look out from a window at a memorial complex attending the 20th anniversary of the NATO bombing in the village of Glogjan, Kosovo on March 24, 2019. AP Kosovo: Remembering the war, 20 years on Kosovo Albanian children place Albanian flags on the graves at memorial complex during the 20th anniversary of the NATO bombing in Glogjan. AP Kosovo: Remembering the war, 20 years on Kosovo Albanians mourn during the ceremony to mark the 20th anniversary of 113 men killed during the 1998-99 war in the village of Krusha e Vogel, Kosovo, 26 March 2019. EPA Kosovo: Remembering the war, 20 years on Some 113 Kosovo Albanian men of the village were separated from their families and executed on 26 March 1999 by Serb security forces, 45 of them are buried and 68 still missing. EPA Kosovo: Remembering the war, 20 years on A man walks past the graveyards at the cemetery in Krusha e Madhe. AFP/Getty Kosovo: Remembering the war, 20 years on A woman mourning during the ceremony to mark the 20th anniversary of the people killed in the village of Krusha e Vogel. EPA Kosovo: Remembering the war, 20 years on A woman with a child walks past a train that was used to ferry thousands of Albanians out of Kosovo. Reuters Kosovo: Remembering the war, 20 years on These trains took people into North Macedonia during the 1999 NATO bombing in Blace, Kosovo. Reuters

Russia and Serbia blamed Nato and the European Union for the tensions in Kosovo on Wednesday.

Sergei Lavrov, the Russian foreign minister, said the raid on Tuesday was instigated by “those who want to create a buffer zone from Russia on the Balkans” and who “want to push everyone to Nato”.

Speaking to reporters in Slovenia where he was on an official visit, Mr Lavrov said the two bodies “hold sway” over the authorities in Kosovo.

Aleksandar Vucic, the Serbian president, accused Nato-led peacekeepers in Kosovo of “lying” when they said they had informed Belgrade in advance of the police action. He also criticised them for insisting Tuesday’s raid in the north was a regular police operation.

“Nato should do its job, and when they don’t do it, there are others who will,” Mr Vucic warned.

“They are not telling the truth. The situation for the Serb population in Kosovo is much worse than it was up until yesterday.”

Serbian President Aleksandar Vucic says Albanians 'didn't want to compromise' over Kosovo army

The KFOR peacekeeping mission spokesman, Colonel Vincenzo Grasso, said he had been informed days before the raid.

“That was not a surprise. Everybody was informed. That was on the news,” he said.

The EU’s top diplomat Federica Mogherini urged Kosovo and Serbia to return to the negotiating table and normalise relations amid tensions.

She warned about “the risk of the dark forces of the past coming back, in terms of confrontation, even of conflict” if the two sides continue facing off.

Thousands of people gathered on Wednesday at a rally in the northern, Serb-dominated part of the divided city of Mitrovica to protest the arrests.

The protesters waved Serbian flags and banners with the names of those who were detained.

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Serbia and allies Russia and China do not recognise Kosovo’s 2008 declaration of independence, while the UK and more than 100 other countries do.

The lingering dispute has stalled both countries’ efforts to become EU members.