By
Laurence Norman

Updated Aug. 11, 2014 11:18 a.m. ET

Kosovo launched a major operation Monday morning against suspected domestic militants who have fought in Syria and Iraq, arresting at least 40 people and seizing weapons and explosives in dozens of locations, authorities said.

The move is the biggest action yet against suspected militants in Kosovo, where the government has long played down concerns about the threat posed by extremists.

Speaking on condition of anonymity, a government official said the arrests came several months after authorities were warned by a foreign intelligence agency of a possible terrorist attack in Kosovo.
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However, a police statement said only that Monday's arrests targeted people who had fought in Syria and Iraq for the Sunni extremist groups A-Nusra Front, an al Qaeda affiliate that espouses global Islamic rule, and Islamic State, which has recently captured swaths of territory in Iraq.

"I have authorized last night an extensive operation to locate and arrest suspected members of groups who fought in Syria and Iraq. I can confirm that 40 people were arrested so far and explosives, weapons and other material was found in some of the 60 locations that were searched during this operation," Prime Minister Hashim Thaçi said in a statement to The Wall Street Journal.

Kosovo, which declared independence in 2008, has a majority Albanian Muslim population. The government enjoys close relations with the U.S. and other western countries and the constitution enforces a clear division between religion and state.

However, there have long been reports that Kosovars had gone to fight for militant groups in Syria and Iraq. In recent months, police have stepped up arrests as videos and images have circulated of Kosovo men involved in the fighting. Last month, images emerged purporting to show a Kosovar fighter carrying out beheadings.

On Monday, police said that 16 locals are believed to have died in the Syrian and Iraqi conflicts.

Police said the operation against extremists will continue, targeting those who join terrorist groups inside or outside the country and people who support, finance or recruit them. The government official said authorities were preparing charges against several Imams for inciting hate crimes.

In a telephone interview Monday, Mr. Thaçi said authorities believe the number of Kosovars fighting in Iraq and Syria number in the dozens, not in the hundreds.

Mr. Thaçi said a "small number of young people" have been encouraged to fight because of propaganda in social media and because of the influence of a "few individual Imams." He said the government is working closely with the U.S., Turkey and the EU to contain the problem.

Kosovo President Atifete Jahjaga met with senior western diplomats in Pristina on Monday to inform them about the crackdown, according to a western diplomat.

There has been growing concern among European governments about the terror risks posed by young men returning from fighting in Iraq and Syria.

Authorities believe a French man suspected of killing four people at the Jewish Museum in Brussels in May, had returned to Europe after fighting in Syria.

European authorities estimate that as many as 2,000 European men have traveled to Syria to fight alongside rebels in the battle to unseat President Bashar al-Assad.

The U.S. and European countries fought a 1999 war to force former Serbian strongman Slobodan Milosevic to pull his forces out of Kosovo, where a brutal ethnic-cleansing campaign against the mostly-Muslim majority left thousands dead and some 750,000 people driven from their homes.