Croatia's Foreign and European Affairs Ministry on Wednesday forwarded a protest note to Serbia's Ambassador in Zagreb, Stanimir Vukicevic, over incidents in which Croatian handball fans were injured in Novi Sad and Ruma, the ministry said in a statement.

Ambassador Vukicevic expressed regret at the incidents and informed Zagreb that the Serbian authorities had so far arrested six assaulters, Hina news agency reports.

According to him, an investigation is under way and the Croatian side will be informed about its findings in a timely fashion.

The Croatian authorities and the Serbian ambassador agreed that such incidents did not contribute to the strengthening of bilateral relations.

Croatia has requested Serbia to step up security during the forthcoming matches within the ongoing European Championships. The 2012 EHF European Men's Handball Championship is being held in Serbia on January 15–29 in the cities of Belgrade, Nis, Novi Sad and Vrsac.

After a match between Croatia and France on Tuesday evening, Croatian supporters were exposed to a series of serious and organised attacks in Novi Sad and Ruma. One of the Croatian fans was stabbed and admitted to hospital in Novi Sad. This gravest incident occurred in Ruma at a gas station where a Croatian van was set on fire.

Shortly before that, in a Novi Sad suburb, a line of Croatian fans' cars was stoned by about 50 masked youths, one of whom used an axe. Several Croatians were injured and one was hospitalised.

Novi Sad police spokeswoman Mileva Tomic told Beta news agency that about 15 Croatian cars were damaged on a number of locations in the city but the exact number had not yet been determined.

Serbian Police Director Milorad Veljovic last night apologised to the Croatian fans assaulted in Novi Sad and Ruma, saying police would be at their disposal "day and night."

Croatian fans supporting the national handball team were first attacked on Sunday, when two were lightly injured.