Updated

Police have detained 15 suspected Al Qaeda militants who were allegedly planning to attack the U.S. Embassy in Ankara, Turkey's capital, the state-run news agency said Wednesday.

Turkey's Interior Ministry confirmed the capture of suspected Al Qaeda militants, but would provide no other details about the case. U.S. officials said they have contacted Turkish officials about the arrests, which came several days before U.S. Secretary of State Hillary Rodham Clinton is to visit Istanbul, Turkey.

Citing unidentified official sources, the Anatolia news agency said police captured the 15 suspects in Ankara, the western city of Bursa and the nearby town of Yalova, and seized 700 kilograms (1,500 pounds) of chemicals used in bomb making, two assault rifles, ammunition and maps of Ankara.

The suspects were planning to attack the U.S. Embassy in Ankara and unidentified foreign targets, the news agency said. They were brought to police headquarters in Ankara on Tuesday night and were being questioned by anti-terror police, the report said.

The police raids came after a six-month surveillance of a key suspect who is believed to have received training with arms and explosives and rented a two-story house in Sincan town on the outskirts of Ankara, Anatolia said. The police captured the suspect on a street of Sincan earlier this week to avoid a possible clash during a raid, the news agency said.

Turkish media have speculated that homegrown radical Islamic militants affiliated with Al Qaeda are preparing to avenge the May 2 killing of Al Qaeda leader Osama bin Laden in the Pakistani garrison town of Abbottabad by U.S. forces.

In Washington on Wednesday, U.S. State Department spokesman Mark Toner said: "We've obviously seen the press reports. I'm aware that our embassy is in touch, as they always are, with Turkish authorities about these arrests."

Clinton is to visit Istanbul on Friday and Saturday to meet with the Libya Contact Group, which includes more than 40 nations that are participating in or are backing the NATO mission supporting opponents of Libyan leader Moammar Gadhafi. Clinton also will meet with Turkish officials to discuss Libya, Syria and the Mideast peace process.

Al Qaeda's austere and violent interpretation of Islam receives little public backing in Turkey, a predominantly Muslim but officially secular country.

However, Al Qaeda and several other radical Islamic groups have been active in Turkey before.

In June, police arrested 10 suspected Al Qaeda militants in the southern Turkish city of Adana, which is home to the Incirlik Air Base used by the United States to transfer noncombat supplies to Iraq and Afghanistan. Authorities have said Islamic militants tied to Al Qaeda planned to attack Incirlik in the past but were deterred by high security.

Turkish authorities have said dozens of Turkish Islamic militants have received training in Afghanistan.

In 2008, an attack blamed on Al Qaeda-affiliated militants outside the U.S. Consulate in Istanbul left three assailants and three policemen dead.

In 2003, homegrown Islamic militants tied to the Al Qaeda attacked the British Consulate, a British bank and two synagogues in Istanbul, killing 58 people.