Three police officers were killed and at least 20 others were injured in clashes early Saturday between security forces and an armed group in the town Kumanovo in northern Macedonia, local media reported.

The TV station Telma said three officers were killed in an exchange of gunfire. The station said it had confirmed the deaths with family members of the deceased.

Interior Ministry spokesman Ivo Kotevski earlier said police had clashed a "well-trained terrorist group" which had entered Macedonia from an unspecified neighboring country with a plan to "perform attacks on state institutions."

He refused to give details about possible casualties, saying the operation was still ongoing.

However, the U.S Embassy in Skopje issued a statement saying it "deeply regret(s) the loss of life."

"We are following the situation and are in close contact with the authorities and political leaders. We urge citizens to remain calm and allow the facts to be established," the embassy said in a statement.

Kumanovo is an ethnically mixed town located about 40 kilometers (25 miles) northeast of the capital Skopje, near the border with Kosovo and Serbia. The region was the center of hostilities between ethnic Albanian rebels and government forces during the ethnic conflict in 2001.

Ethnic Albanians, who make up a quarter of Macedonia's 2 million people, took up arms in 2001 demanding more minority rights. The conflict ended after six months with a western brokered peace deal that granted more rights to the ethnic Albanian minority.

Kotevski on Saturday said the armed 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 search house to house very carefully", Kotevski said.

Local TV stations aired video footage showing black smoke rising from houses in the western Kumanovo suburb and many civilians fleeing the area.

Macedonian President Gjorge Ivanov urgently ended his visit to Russia and is on his way back home. The president's office said he will call for a National Security Council meeting in relation with the latest security developments.

The EU delegation in Macedonia appealed for calm and said in a statement it is waiting "for facts to be established by the relevant authorities."

Serbia, Macedonia's northern neighbor, reacted by sending reinforcements of special police to the border region, apparently fearing a possible spillover of tensions.

The incident came a day after thousands of opposition supporters joined nationwide protests against alleged police brutality in Macedonia. The protests started after opposition leader Zoran Zaev — citing illegally recorded conversations — accused the government of trying to cover up the 2011 police killing of a 22-year-old man.

The recordings are part of a series of wiretaps Zaev has been releasing amid Macedonia's most severe political crisis in years.

Zaev on Saturday appealed for calm, but had earlier called for a large anti-government protest on May 17.

The junior coalition partner in the conservative government, the ethnic Albanian Democratic Union for Integrations, or DUI, has also expressed concern and appealed for calm. DUI urged people not to respond to provocations.

___

Testorides reported from Skopje. Jovana Gec in Belgrade, Serbia, contributed to this report