Turkish anti-terrorism police in Adiyaman break a door during a nationwide operation Feb. 5 targeting suspected Islamic State networks. (Mahir Alan/Associated Press)

Turkey’s Interior Ministry said Monday that it had detained more than 800 people in a week-long security operation against the Islamic State, underscoring the rising alarm about the militant threat after deadly attacks.

Most of the 820 suspects were detained Sunday in raids carried out in 29 cities, the statement said, but it gave no details about their suspected connections to the Islamic State.

It was thought to be the largest operation by the Turkish authorities against the militant group and came five weeks after the Islamic State claimed links to a rampage by a gunman who killed dozens of people at a nightclub in Istanbul as revelers welcomed 2017.  

Turkey has steadily intensified its anti-terrorism operations since December, when it was shaken by attacks that came in rapid succession. They included the car bombing of a stadium in central Istanbul, claimed by Kurdish militants, and the assassination of Russia’s ambassador to Turkey in Ankara, the capital.

In a scene captured by journalists, the diplomat’s assassin, Mevlut Mert Altintas, invoked the bloodshed in the Syrian city of Aleppo as the stricken ambassador, Andrei Karlov, lay nearby.

Turkey’s own deepening military involvement in the Syrian war has led to widening political divisions at home and exposed it to a growing threat of retaliation from the Islamic State. Turkish troops launched an offensive last summer against the Islamic State-held town of Jarabulus. For the past few months, the Turkish military has taken heavy casualties as it attempts to dislodge the militant group from al-Bab, a border town in Syria.

Turkish President Reçep Tayyip Erdogan — one of the region’s most stalwart backers of rebel groups fighting against the Syrian government — has more recently shifted course. Turkey has teamed up with Russia, an ally of Syrian President Bashar al-Assad, in trying to negotiate a political settlement to end the nearly six-year-old conflict.

In November, Abu Bakr al-Baghdadi, the Islamic State’s leader, released an audio message calling on followers to add Turkey to “your list of battlefields.” 

After the New Year’s Day assault on the Reina nightclub, the Islamic State released a statement framing the killings as retribution for Turkish shelling and airstrikes on the militant group in Syria.