Syrians living in Istanbul hold candles at the site of Tuesday’s suicide bomb attack at Sultanahmet square in Istanbul, Turkey January 13, 2016.

Turkish land forces have fired nearly 500 times on ISIS targets in Syria and Iraq, killing almost 200 militants in response to a suicide bombing in Istanbul which killed 10 German tourists, Prime Minister Ahmet Davutoglu said on Thursday.

Turkey will also carry out air strikes against the radical Sunni group if necessary and will maintain its “determined stance” until ISIS fighters leave its border areas, Davutoglu told a conference of Turkish ambassadors in Ankara.

The bomber blew himself up on Tuesday among groups of tourists in the historic center of Istanbul. Davutoglu said on Wednesday he was a member of ISIS who had entered Turkey from Syria as a refugee.

“After the incident on Tuesday, close to 500 artillery and tank shells were fired on Daesh positions in Syria and Iraq,” Davutoglu said, using an Arabic name for ISIS

“Close to 200 Daesh members including so-called regional leaders were neutralized in the last 48 hours. After this, every threat directed at Turkey will be punished in kind,” he told the ambassadors’ conference.

Turkey, a member of the NATO military alliance and the U.S.-led coalition against ISIS, has repeatedly said it wants to flush ISIS from a zone in northern Syria just across its border.

Turkish war planes have not flown in Syrian air space since Turkey shot down a Russian fighter jet in late November, triggering a diplomatic row with Moscow, which is also conducting air strikes in Syria.

Seven suspects arrested

Meanwhile, Turkey has arrested a total of seven suspects over a suicide bombing blamed on ISIS 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.

Ala said the figure included five previously announced arrests: four who were detained Wednesday in relation to the attack and one who was detained on Tuesday evening.

He did not give any details about the two new detentions.

A 28-year-old Syrian member of ISIS blew himself up Tuesday in Sultanahmet Square, home to Turkey’s most visited historic sites, including the Ottoman-era Blue Mosque and the Hagia Sophia, a former Byzantine church that was turned into a mosque before later becoming a museum.

Turkey has kept an open border to refugees from Syria’s civil war and is now home to more than 2.2 million, the world’s largest refugee population. But its border has also been used by foreign fighters seeking to join ISIS or return from its ranks to commit atrocities abroad.

“This individual was not somebody under surveillance. He entered Turkey normally, as a refugee, as someone looking for shelter,” Davutoglu told a news conference, adding he had been identified from fragments of his skull, face and nails.

“After the attack his connections were unveiled. Among these links, apart from Daesh, we have the suspicion that there could be certain powers using Daesh,” he said, using an Arabic name for ISIS.

Turkey accuses Syrian President Bashar al-Assad, and his allies including Iran and Russia, of cooperating with ISIS in the Syrian regime’s effort to destroy Syrian opposition forces.

Turkey, which like Germany is a member of the U.S.-led coalition against ISIS, has become a target for the radical militants.

It was hit by two major bombings last year blamed on the group, in the town of Suruc near the Syrian border and in the capital Ankara, the latter killing more than 100 people in the worst attack of its kind on Turkish soil.

Related articles across the web

• Visa Waiver Agreement Between Turkey and Syria Abolished
• Netherlands hits back at "completely absurd" Assad assertions
• Russia open to Assad's ouster after Syria transition, diplomats
• US brings ambitious Syria peace plan to UN
• Putin: Turkey's downing of Russian plane an 'enemy act'
• Turkish PM reiterates right to defend airspace
• For Syria! For Assad!
• Amnesty Calls for Release of Journalists Can Dündar and Erdem Gül
• UN chief downplays Assad's role in peace process
• Welcome to Turkey!