The suspects, all Turks, reportedly fled the country after the attacks, which targeted two synagogues in near-simultaneous bombings Nov. 15 and the British consulate and a British bank in twin attacks five days later. A total of 61 people were killed.
Citing a statement from paramilitary police, Anatolia said the suspects included Hilmi Tuglaoglu (search), a close associate of Azat Ekinci, a central suspect in the blasts.
News reports have named Ekinci as a key accomplice in the synagogue bombings, saying he used fake identities and cash to buy pickup trucks that were packed with explosives. The reports said Ekinci had traveled to Iran, received military and explosives training in Pakistan between 1997-99 and fought in Chechnya.
The suspects were being questioned, the statement added. There were no details about Tuglaoglu's alleged involvement, though police said his wife was also brought from Syria.
The report came amid signs of progress in the investigation.
A Turkish court on Saturday charged a key suspect captured last week with trying to overthrow Turkey's "constitutional order" -- a crime equivalent to treason. The first major suspect to be charged in the attacks, he is accused of having given the order to carry out the truck bombing of the Beth Israel synagogue.
Police identified him by his initials, Y.P., but nearly all major Turkish newspapers said he was Yusuf Polat. The daily Radikal said he was born in 1974 in Turkey's southeastern province of Malatya.
The daily Milliyet and other newspapers reported Sunday that Polat and others confessed to belonging to a 10-man cell that was an extension of the Al Qaeda terror network. Police also had evidence that the attackers received support domestically and from abroad, Milliyet reported.
Newspapers reported that members of the cell, including several of the homicide bombers, had met while training in Afghanistan, and that Polat fought in Afghanistan.
Istanbul Gov. Muammer Guler did not directly address the news reports but said there were "resemblances to an Al Qaeda link" in the attacks.
"However, we have to obtain all the official evidence, all the links, all the clues. It wouldn't be right to talk about the links without all the official evidence," Guler said.
He added there was no evidence yet linking the attacks to the militant Turkish Islamic group, Hezbollah, which is not linked to the Lebanese group of the same name.
Police refused to comment on the reports. They said only that Y.P. was arrested Tuesday at an Iranian border crossing in eastern Agri province, and that he had gone to the Beth Israel synagogue before the attack and ordered its start.
Turkey has long accused Iran's government of fueling radical Islam in Turkey and has alleged that members of an Islamic radical group suspected in a series of killings trained in Iran and received support from its government.
The daily Hurriyet said Y.P. was tracked down through his cell phone records after allegedly calling a homicide bomber minutes before the attack. The Anatolia news agency reported Sunday that materials used to make bombs were found in a house in Istanbul that he used.
Authorities have charged another 20 people in connection with the blasts, but for lesser roles. All the homicide bombers were Turks.
Guler announced Sunday that the attack against the HSBC bank's Istanbul headquarters was carried out by Ilyas Kuncak, born in 1956 in the capital Ankara. Anatolia had earlier named the bomber as Mevlut Ugur and newspapers previously named two other suspected militants.
He also confirmed that Feridun Ugurlu carried out the attack against the British consulate. Ugurlu is believed to have fought with Islamic radicals in Afghanistan and Chechnya and his role had widely been reported by Turkish newspapers.
Police have been focusing on Turkish fighters who battled in Chechnya, Afghanistan or Bosnia in the investigation.
Western and Turkish officials say the homicide attacks bore the hallmarks of Usama bin Laden's Al Qaeda and there have been at least three claims of responsibility claiming to be from the terror network. However, Turkish officials have said it was too early to say for sure that Al Qaeda was behind the attacks.
American counterterrorism officials said last month that several senior Al Qaeda operatives who fled to Iran after the U.S.-led war in Afghanistan ousted the Taliban may have developed a relationship with a secretive military unit linked to Iran's religious hard-liners.
Iran has said it has some Al Qaeda operatives in custody but has refused to identify them or provide other details.