Authorities in Macedonia say police have clashed with an "armed terrorist group" in the northern town of Kumanovo and parts of the town have been sealed off.

Macedonia's state-run news agency MIA reported that four police officers were injured by gunfire, and three of them were taken to a hospital in the capital, Skopje.

Interior Ministry spokesman Ivo Kotevski refused to give more details to reporters about possible casualties in the incident, referring to the operation as being ongoing.

He said that a "well-trained terrorist group" had entered Macedonia from an unspecified neighboring country with a plan to "perform attacks on state institutions." He said the group was "sheltered in the houses of supporters" in the Kumanovo neighborhood Diva Naselba, but didn't give any more details about the organization.

Police launched a search operation in that area early Saturday morning and Kotevski said "terrorists" attacked special police forces with automatic guns, snipers and bombs.

"This is a risky operation because it is an area with narrow streets and police need to perform house-to-house searches very carefully", Kotervski said.

The incident came a day after thousands of opposition supporters joined nationwide protests against alleged police brutality.