ISTANBUL, Turkey — The police have detained 15 suspected Al Qaeda militants on evidence that they had plotted to attack foreign diplomatic targets including the United States Embassy in Ankara, Turkey, the Anatolian News Agency reported on Wednesday.

Security operations leading to the arrests were conducted in Ankara, the capital, and in Yalova and Bursa, two religiously conservative towns in western Turkey. The operations were based on the statements of a leading suspect who was captured in Ankara after being watched by the authorities for six months, the report said.

According to the report, the Ankara police seized more than 1,500 pounds of chemicals used to make bombs, along with two assault rifles, bullets, documents and maps at the two-story house belonging to the suspect, who they said had received military training in explosives and arms outside the country.

His statements to the police led to the arrests of nine other suspects in Ankara, three in Bursa and two in Yalova in raids on Tuesday, the news agency said.