Five Macedonian policemen were killed and more than 30 others injured in a major operation against armed group, Macedonian Interior Minister Gordana Jankuloska said Saturday evening.

"This is a very difficult operation... one of the most difficult that the Macedonian police have ever encountered," Jankuloska told a press conference on the operation conducted in the highly populated town of Kumanovo, an ethnic Albanian area of northern Macedonia.

The operation by police started at 4 am local time on Saturday morning and was targeted at disarming and arresting members of an armed group.

Police intelligence indicated that the group members entered Macedonia illegally from the neighboring Kosovo region and was preparing "terrorist attacks" against state institutions, according to officials.

The operation is still underway and no immediate details are released on the number of killed and arrested terrorists or civilian casualties.

"The situation is still high-risk. A number of terrorists are from Macedonia, but the others are from one neighboring country", Jankuloska added.

Macedonian police said the "terrorists" were extremely dangerous and engaged in fierce combat with the police using snipers, bombs and other weapons.

Authorities in Kosovo condemned "the violation of order and security by any individual or group with destabilizing aims in Macedonia."