A suspected Islamic State militant planning what Turkish authorities have labeled “a sensational attack” was detained in Istanbul, the state-run Anadolu news agency reported Tuesday. Details were scant; the militant, identified solely by the initials H.S., was apprehended in a raid on a hotel in the city’s Kucukcekmece suburb. The man’s nationality was not revealed but he had crossed illegally in to the border province of Gaziantep from Syria and was in possession of an automatic rifle, ammunition and spare magazines. He had staked out Istanbul’s central Taksim Square, frequented by tourists and home to numerous bars, in apparent preparation for the attack, Anadolu reported.

Police detained six other suspected IS militants in the central Anatolian province of Kayseri in dawn raids, the English-language Daily Sabah reported.

No information about their provenance or plans is available. Coming on the heels of a separate anti-IS raid in the province of Bursa this month, the arrests point to Turkey having a festering IS problem. The most recent Defense Department inspector general’s report on the US military mission in Iraq and Syria called its NATO ally a “a major facilitation hub” for IS operatives, financing and weapons. It acknowledged, however, that Turkey was doing more in recent years to counter IS as the group seeks to resurrect itself in Iraq and Syria.

Turkey designated IS as a terrorist organization in 2013, but it has long been accused of serving as “a jihadi highway” with security forces looking the other way as thousands of foreign fighters and Turkish nationals flowed illicitly through its porous 911-kilometer (566-mile) border with Syria.