Turkish police detained four Islamic State suspects as part of an investigation into a possible attack on the U.S. Embassy in Ankara, the country’s state-run news agency reported on Monday.

The arrests came as the embassy was closed on Monday over an unspecified security threat.

The Anadolu Agency said police detained four Iraqi nationals in connection with the threat against the embassy. Two of them were detained on a bus at a security check on a highway linking the Black Sea city of Samsun to Ankara. Two others were detained in Samsun by police acting on information they provided, the report said.

The agency identified the suspects by their first names only.

Security was high outside the U.S. embassy on Monday, and police searched pedestrians before allowing them to enter a street where the main gate is located.

The U.S. embassy said on its web page late on Sunday that the mission would be closed due to a security threat, and urged U.S. citizens to avoid the embassy as well as large crowds. It also advised citizens to “keep a low profile.”

Turkish Deputy Prime Minister Bekir Bozdag said the U.S. Embassy had shared intelligence with Turkey’s intelligence and security authorities, leading to “important results.” He said the U.S. diplomatic missions in Istanbul and the southern city of Adana remained open for business.

The Ankara governor’s office said authorities had reviewed security in the capital and had taken additional measures, following intelligence provided by U.S. “sources” about possible attacks against the embassy or where Americans are staying.

Earlier on Monday, police detained 12 IS suspects in Ankara and were searching for eight others, Anadolu reported, although it was not clear if these arrests were linked to the threat against the U.S. Embassy.

The Ankara chief prosecutor’s office said in a statement that all of the suspects captured in the police operation were foreign nationals. They were allegedly trying to recruit members for the Islamic State group and were in contact with people in “conflict zones,” the statement said, without provide further details.

In 2013, a suicide bomber detonated an explosive in front of the U.S. Embassy in Ankara, killing himself and a Turkish guard. Turkish officials blamed the attack on domestic leftists.

Turkey suffered a slew of deadly terror attacks in 2015 and 2016 carried out by IS or Kurdish rebels. An attack at a luxury Istanbul nightclub during New Year celebrations on Jan. 1, 2017, killed 39 people.

Bozdag said Monday that IS extremists had carried out 20 attacks in Turkey, killing a total of 310 people and wounding 967 others.

Turkish authorities arrested a total of 4,043 IS militants between 2011 and 2018, Bozdag added. Close to 2,000 of them were “foreign terrorist fighters,” the minister said.

(AP)