Turkey has arrested a total of seven suspects over a suicide bombing blamed on the Islamic State (IS) group that killed 10 German tourists in Istanbul, the Turkish interior minister said Thursday.

"Our operations are continuing. The number of those detained so far has risen to seven," Efkan Ala told Turkish ambassadors gathered in Ankara.

They came in the hope of enjoying Istanbul's sights in the relative peace of the low season. But Tuesday's suicide attack in the heart of the city's historic Sultanahmet area left tourists reeling.

'This is the first time that I've been afraid for my life while on holiday," said French tourist Nathalie Julien after the attack blamed by Turkish authorities on the Islamic State (IS) group.

Turkish authorities arrested three people over the death of a Syrian filmmaker who was assassinated in southern Turkey after producing anti-Islamic State documentaries, the state media said Sunday.

Naji Jerf, 37, was shot dead in broad daylight in Gaziantep province late December by assailants using a silencer outside a building that houses Syrian opposition news outlets.

Turkish troops have killed 18 members of the Islamic State (IS) group after the jihadists launched an attack on a camp used to train Iraqi fighters outside the Iraqi city of Mosul, President Recep Tayyip Erdogan said Friday.

Turkish forces have been using the Bashiqa camp, just outside Mosul, to train local Iraqi fighters to retake the city from IS.

Turkish police on Friday raided the offices of the main pro-Kurdish party in central Istanbul, making arrests and seizing documents.

Riot police blocked the entry to the street where the Beyoglu district office of the Peoples' Democratic Party (HDP) is located while anti-terror police conducted a search, an AFP photographer said.

Turkey said on Thursday it had summoned Iran's ambassador to protest attacks on Turkish President Recep Tayyip Erdogan in the Iranian press in the wake of a diplomatic crisis between Tehran and Riyadh.

Erdogan has refused to condemn Saudi Arabia's execution of prominent Shiite cleric and activist Sheikh Nimr al-Nimr this month. The execution sparked outrage in Shiite-majority areas of the Middle East, and protesters in Iran attacked two Saudi diplomatic missions, prompting Riyadh to sever diplomatic ties.

A mortar attack was the cause of a deadly incident on December 23 at Istanbul's Sabiha Gokcen airport that left one person dead and damaged several planes, Turkish prosecutors said on Thursday.

Four mortar shells were fired from a forested area around two kilometers (1.25 miles) from the airport, prosecutors said in a statement carried by the Anatolia news agency.

Turkish President Recep Tayyip Erdogan on Wednesday refused to condemn Saudi Arabia for its execution of 47 convicts including a prominent Shiite cleric, saying it was an "internal legal matter" of the kingdom.

"The executions in Saudi Arabia are an internal legal matter. Whether you approve or not of the decision is a separate issue," Erdogan said in a televised speech, his first reaction to the controversy which has raised tensions between Saudi Arabia and its regional rival Iran.

A U.S.-based Turkish preacher who has emerged as an arch-enemy of President Recep Tayyip Erdogan went on trial in absentia Wednesday along with several former police chiefs charged over the corruption allegations that hit the Turkish leader in 2013.

Fethullah Gulen, a former ally of Erdogan turned chief foe, was not present at the start of the proceedings in Istanbul, with Washington failing to grant Turkish requests for his extradition from his secluded compound in Pennsylvania.

The Turkish coastguard conducted an unprecedented operation to seize 13 tons of marijuana in powdered form from a Bolivia-registered ship off the Libyan port of Tobruk, the interior ministry said Wednesday.

Turkish coastguards followed the Bolivian vessel with a plane and a ship after receiving a tip-off, Turkish official media said, quoting the interior ministry.