Police sources say suspects wanted to conduct five terror attacks at different locations in Turkish city.
The suspects, together with a bomb-laden vehicle and motorcycle, were found in the car park of the Forum Istanbul shopping mall in the city’s European-side Bayrampasa district.
A police source, who spoke on condition of anonymity, said the suspects were planning to attack celebrations being held to mark Turkey’s Republic Day on Oct. 29.
In a series of new details, the police told Anadolu Agency the group was planning four suicide attacks at different locations in the city on the same day.
Police acted after the suspects attempted to destroy two safe houses on Friday.
In a property in Istanbul's Esenyurt district, police found four gas canisters, two plastic jerrycans full of chemicals, two more of gasoline, large amounts of ammonium nitrate, steel ball bearings and other bomb-making materials.
On Friday, in another property in the city’s Arnavutkoy district, police also seized similar equipment the gang had attempted to destroy.
The suspects tried to destroy evidence, the source said, by attempting to burn the safe houses after they prepared the car bomb.
Four suicide vests, two firearms, ammunition and ammonium nitrate were also found in the vehicle and motorcycle seized by police on Saturday.
The suspects will be questioned in the coming days, police sources said.
Interior Minister Suleyman Soylu, speaking to reporters in the southwestern province of Antalya on Tuesday, said counterterrorism operations targeting Daesh in both Istanbul and across Turkey were ongoing: “As of this week, we had over 300 Daesh targets [to eliminate]. Our colleagues have had taken important steps in this period.”
Turkish security forces have been involved in a long-running campaign to thwart Daesh attacks.
Since August last year, Istanbul police have carried out over 100 operations and detained close to 1,000 suspects.
On Aug. 27, 2016, a suspect was detained accused of planning to attack a store selling books on Christianity as well as the HQ of a local political party in Istanbul.
On Nov. 30, 2016, police arrested a suspect in Istanbul who was planning an attack on the Turkish parliament building in Ankara as well as religious centers.
Operations across Turkey have also seen terrorist suspects detained.
On July 5 this year, Turkish police arrested six people suspected of planning to attack a protest march being led by the head of the country's main opposition party.
On May 21, two foreigners were killed in an anti-Daesh operation in Ankara. Governor Ercan Topaca said the terrorists had planned to attack the Justice and Development (AK) Party’s extraordinary congress to be held later that day.
Three days earlier, eight suspects allegedly planning to conduct attacks on events in Izmir, Istanbul, Erzurum and Mardin during Turkey’s May 19 national holiday, were arrested.