Turkey detained three Russians on suspicion of links to ISIS on Wednesday, following a bomb attack that killed 10 foreign tourists in Istanbul, according to a senior courthouse source and local media reports.
The trio were taken into custody near the southwestern resort city of Antalya and were being questioned, the official at the city's courthouse told NBC News on condition of anonymity.
Russian and Turkish state-run news agencies also said the suspects were accused of having links to ISIS.
Turkey's Interior Minister Efkan Ala said Wednesday another person had been arrested in direct connection with the bombing without giving any more details, according to The Associated Press.
Ten people, mostly Germans on vacation, died in Tuesday's attack in the heart of Istanbul, close to the city's iconic Hagia Sofia and Blue Mosque.
Turkey said the alleged bomber was a Syrian-born ISIS militant born in 1988.
Alexander Tolstopyatenko, the Russian Consul General in Antalya, confirmed to several of his country's state-run news agencies that three Russian citizens had been detained. "The reasons for their detention are being clarified," he told the state-run TASS news agency and others.
During Wednesday's detentions, Police also seized documents and CDs during a search of their building where the suspects were staying, Turkey's Dogan News Agency said according to a translation by Reuters.
Turkey is a powerful member of both NATO and the U.S.-led coalition against ISIS. Its relations with Moscow frayed dramatically after it shot down a Russian jet it said infringed on its airspace in November.