Kosovo authorities say they have cut off the water supply to tens of thousands of people in the capital after police arrested five suspects linked to the Islamic State group who allegedly were planning to poison a reservoir.

Pristina's water authority says the water supply was stopped early Saturday "because of security issues" and that water samples are being tested for any suspicious substances.

Police say officers patrolling the Badovac reservoir saw three of the men, whose identities haven't 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.

Police have been on alert in recent weeks after Kosovo-born volunteers appeared on IS propaganda videos warning of imminent attacks against targets including water supplies.