Security forces captured 16 Daesh suspects in operations against the terrorist group on Monday. The Ankara Public Prosecutor's Office announced earlier that it had issued detention warrants for 20 suspects and the search was underway to capture the others.

Operations came hours after the U.S. Embassy in the capital announced its closure for Monday due to a security threat. The embassy, on March 5, advised U.S. citizens in Turkey to avoid large crowds and the embassy building and to be aware of their own security when visiting popular tourist sites and crowded places.

The Ankara Governor's Office released a statement later that said the city has taken additional security measures upon receiving intelligence from U.S. sources. Media reported that the operation targeting Daesh was planned well before the U.S. sources warned the local authorities about the threat.

All suspects were foreign nationals, although officials did not specify their nationalities. They are accused of recruiting for the terrorist group and having contacts with Daesh members in Syria and Iraq.

Later on in the day, police detained four other Daesh terrorist suspects allegedly planning an attack on the U.S. Embassy in Ankara on the Samsun-Ankara highway.

All four suspects were identified as Iraqi nationals and were nabbed by police as they were heading to the capital from northern Samsun province, reports said.

Police reportedly confiscated digital material after raiding the houses of the terrorists.

Security was high outside the embassy on Monday, and police searched pedestrians before allowing them to enter a street where the main gate is located. The U.S. Embassy was the target of a suicide bombing in 2013 by a militant from the Revolutionary People's Liberation Party-Front (DHKP-C), which killed a Turkish security guard.

Meanwhile, Deputy Prime Minister Bekir Bozdağ said that Turkey is the country most effectively fighting against Daesh.

A total of 3,000 Daesh terrorists were killed in Operation Euphrates Shield in Syria, Bozdağ said, while 1,000 others were killed trying to attack the Turkish camp in Iraq's Bashiqa. Moreover, 12,538 suspects, including 5,654 foreigners, were detained between 2011 and 2018 for links to Daesh.

Additionally, 4,043 terrorist fighters, including 1,858 foreigners, were also detained and 61,158 people from 148 countries were barred from entering Turkey and 6,151 were caught and extradited between 2011 and 2018.

Amid fears that Daesh militants who fled Syria could hit Europe and Turkey, authorities have heightened crackdowns on the terrorist group with almost daily operations to capture suspected militants.Though Daesh lost many strongholds in Iraq and Syria, a controversial deal between Daesh militants and Syrian groups linked to the PKK, a major terrorist group that carries out attacks in Turkey, helped their safe evacuation from Raqqa, Syria. Turkey shares a lengthy border with war-torn Syria and struggles to keep itself safe from infiltration despite a giant border wall that is currently under construction.

The country is at the forefront of efforts to quell threats from the terrorist group, which partly depends on foreign recruits for fighters.Turkey has stopped thousands trying to enter Syria to join the group over the past few years. It is now concerned with militants fleeing Iraq and Syria. The country has stopped 5,800 foreign Daesh recruits on its borders and arrested around 10,000 members of the terrorist group in continuous operations.

Daesh targeted Turkey in a string of attacks in the past three years. The last large-scale Daesh attack was in Istanbul on Jan. 1, 2017. A lone gunman killed 39 people at an Istanbul nightclub during New Year's Eve celebrations. In Ankara, Daesh suicide bombers killed 109 people attending a peace rally near city's train station.