Authorities in Kosovo have cut off water supplies to tens of thousands of people in the capital Pristina after an alleged plot by supporters of ISIL to poison supplies.

Authorities in Kosovo have cut off water supplies to tens of thousands of people in the capital Pristina after an alleged plot by supporters of the so-called 'Islamic State of Iraq and the Levant' (ISIL) takfiri group to poison supplies.

Officials from the city's water board said supply was cut early on Saturday "because of security issues" and that supplies had been tested for suspicious substances.

Al Jazeera Balkans news network reported that the tests carried out by the Kosovo Institute for National Health had detected no sign of toxic content.

The move follows the arrest of five people linked to ISIL, who were accused of planning to poison a reservoir, according to the Reuters news agency.

Police said officers patrolling the Badovac reservoir saw three of the men, whose identities have not been revealed, behaving suspiciously. The reservoir supplies almost half of Pristina, a city of more than 200,000 people. Another two suspects were arrested elsewhere in Kosovo.

Kosovo has been on a heightened state of alert in recent weeks after Kosovan members of ISIL appeared in propaganda videos alongside other members from the Balkans warning of attacks against targets including water supplies.

"If you can, take poison and put it in their meal or in their drink. Make them die, make them die of poisoning, kill them wherever you are...you can do it," one man is heard imploring ISIL supporters.

Kosovo arrested more than 40 people in August last year to prevent them from joining factions fighting in the civil war in Syria.