Turkish police say some of the 155 Islamic State-linked suspects arrested in connection to a foiled plot over the weekend are foreign born.
Counterterrorism officials detained four suspected IS militants for planning Saturday's thwarted attack, two of which are Austrian citizens of Turkish origin, Turkish media reported, citing police sources.
Istanbul police authorities said the IS terror group had planned to target a shopping mall in Istanbul's Bayrampaşa district, which lies on the European side of the city.
According to police, a car loaded with explosives and a bomb-laden motorcycle were found in the parking area of the shopping mall on Saturday.
Turkish media suggested that the attackers might have planned to target Republic Day celebrations on Sunday.
The incident has triggered an anti-IS hunt in major cities across the country, including Istanbul, Ankara and Izmir. Police claimed to have brought down two terror cells in Istanbul.
Turkey has been targeted by IS militants several times during the past two years.
In January, IS claimed responsibility for a New Year's Day nightclub bombing by an Uzbek gunman in Istanbul that killed 39 people and wounded 65 others.
At least 44 people were killed and more than 230 others were injured in suicide bombings at the Istanbul airport in June 2016. Three of the suicide bombers who carried out the deadly attack were from Russia, Uzbekistan and Kyrgyzstan, according to Turkish authorities.
In January 2016, 10 German tourists were killed in a suicide bombing in Istanbul's historic district.
While police have been on high alert to counter any IS attacks, opposition parties have warned about possible future IS attacks. Ozturk Yilmaz, an opposition leader, said that as IS loses ground in Syria and Iraq, the group might try to further its existence by planning attacks within Turkey.