Turkish intelligence services have discovered a plan by the Islamic State of Iraq and al-Sham (ISIS) to attack consulates in Istanbul, and as a result, have stepped up security measures at foreign missions. The militant group active in Iraq and Syria reportedly dispatched a reconnaissance team to Turkey to plan the attacks according to intelligence sources. Targets are said to include U.S., France and Belgian diplomatic missions in Istanbul.

The team of 17 ISIS militants from Syria's Raqqa infiltrated Turkey in December 2014 on separate dates through the Şanlıurfa and Gaziantep provinces on the Turkish-Syrian border as well as via Reyhanlı, a Turkish town located near the border.

Intelligence sources said militants conducted a reconnaissance mission at the U.S., French, Belgian and Syrian consulates in Istanbul. The reconnaissance team was reportedly headed by French national Sufiyan Yasin Amini and employed Turkish-Belgian ISIS militants as interpreters during their stay in Turkey. They were divided into smaller teams and avoided contact with each other to dodge intelligence officials.

Each team visited the consulates under the guise of visa applicants, and checked security measures and potential blind spots for infiltration into consulate buildings. Turkish intelligence officials discovered that militants focused on two booths housing Turkish security guards outside the U.S Consulate, studied a church next to the French Consulate and the hotel next to the Belgian consulate, possibly to use them as launch pads to conduct the attacks. Sources said the militants communicated with each other and ISIS leadership abroad via Skype after the mission was completed.

The Turkish National Police was put on alert across the country after the plot was uncovered. Intelligence services urged security forces to be cautious against "sensational" attacks by ISIS. Turkey, criticized for allowing foreign fighters to join ISIS forces in Syria, is itself under the threat of the radical organization due to its condemning rhetoric against the terrorist organization, and the country has up to 700 of its citizens in ISIS's ranks.

Foreign Minister Mevlüt Çavuşoğlu warned last week that Turkish nationals joining the organization may conduct attacks in Turkey once they return. "A common concern about the foreign fighters is what will happen when they return to their homeland. We have this concern too," he said. Çavuşoğlu has said that Turkey had barred entry to around 7,250 people from abroad who were planning to join the armed faction and 1,160 would-be fighters were also deported.

The country stepped up measures along its 911-kilometer-long border with Syria against infiltration from the war-torn country and vice versa, but Çavuşoğlu has acknowledged that they would never be able to make the border completely watertight.

Turkish media outlets reported that ISIS was behind a suicide bombing at Istanbul's Sultanahmet (Blue Mosque) Square, which killed a police officer earlier this month. However, the group did not claim responsibility for the attack perpetrated by a young Russian woman.