Members of Turkish forces secure the scene of an explosion on the road linking the cities of Diyarbakir and Bingol, in southeastern Turkey, Thursday, Feb. 18, 2016.

One Turkish soldier was lightly wounded on Tuesday after a military outpost in the southeastern province of Gaziantep came under fire from ISIS militants from across the Syrian border, privately owned Dogan News agency said.

Turkey’s military responded in kind and fired artillery into Syria, the agency said.

Turkey, which faces multiple security threats, is on heightened alert after four suicide bombings already this year, two of which have been blamed on ISIS.

Gaziantep province is near the Syrian border and part of it lies just across the frontier from the ISIS-controlled Syrian town of Jarablus.

Meanwhile, authorities in southern Turkey have arrested two men suspected of preparing to carry out suicide bombings for ISIS, which has staged two attacks in Istanbul this year, reports said Tuesday.

The men were arrested in the southern province of Gaziantep, which borders Syria, the local governor’s office said in a statement carried by the Dogan news agency.

One of them was named as Mehmet Mustafa Cevik, described as a member of ISIS and one of its Turkish affiliates, the Dokumacilar Group.

The Dokumacilar Group, named after its wanted founder Mustafa Dokumaci, is the suicide bomber unit suspected of being behind the October 2015 attack that killed 103 people at an Ankara peace rally in Turkey’s bloodiest-ever attack.

The cell has also been linked to the killing of 34 people in the town of Suruc on the Syrian border in July 2015.

The other militant arrested was Ercan Capkin, the brother of Erkan Capkin, one of the suspected suicide bombers behind the March 19 attack on a famous Istanbul shopping thoroughfare that left four people dead.

A dozen German tourists were also killed in January when a suicide bomber linked to ISIS detonated his charge in the heart of Istanbul’s historic center.

Both suspects were ordered by a court in Gaziantep to be held in jail ahead of trial, the report said.

The Turkish interior ministry now has 23 suspected ISIS militants on its most wanted list with a total bounty of 42 million lira ($15 million) on their heads, the Hurriyet daily reported Tuesday.

Three suspected ISIS militants are on its urgently-wanted red list including Mustafa Dokumaci, the alleged leader of ISIS in Gaziantep, Ilhami Bali and Yunus Durmaz who is said to have planned the March 19 attack.

Turkey has been for several months on a state of high alert due to a series of attacks blamed both on ISIS and Kurdish militants amid the resumption of a conflict with the Kurdistan Workers’ Party (PKK).

The attack in Istanbul came less than a week after a car bomb exploded in central Ankara killing 35 people which was claimed by a radical Kurdish faction that split from the PKK.

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