Newspapers said on Thursday though information on the probe has been difficult to obtain due to a state-ordered media blackout, the leader of the armed group was identified as Abu Mussab al-Zarkawi, a suspected ally of Usama bin Ladin.
Hurriyet daily said Zarkawi, a Jordanian, probably guided the group of four bombers who detonated explosives-packed vehicles outside two Istanbul synagogues on 15 November and the British consulate and HSBC bank offices on 20 November.
The newspaper said Zarkawi led an armed group called Hizb Allah, based in mainly Kurdish southeast Turkey, and quoted security sources as saying he and his men got trained in camps in Afghanistan until 2001.
Zarkawi is more widely known as the founder of al-Tawhid, an extremist organisation which aims to overthrow the Jordanian state and kill all Jews.
Aksam daily said police had identified the man who blew himself up outside the HSBC offices, by comparing DNA samples from the scene with those of his brother.
It said his name was being kept secret because he was believed to have played "a key role" in the group he belonged to.
Three more suspects were arrested on Wednesday in connection with the attacks. Defence lawyer Selahattin Karahan said it was not known what charges would be brought against the suspects. The state security court freed 15 others who were being held in the probe.
"If there is a common platform against international terrorism, information about future attacks must be given to the concerned country, not to the media"
Turkish prime minister
To date, 18 people have been charged in connection with the
bombings - 12 over those on 20 November and six over the synagogue blasts - and dozens more have been detained, questioned and released.
PM criticises Britain
Meanwhile, Turkish Prime Minister Tayyip Erdogan accused Britain of not sharing intelligence about possible future attacks with Turkish authorities after London said on Tuesday that "further attacks may be imminent" in Istanbul and Ankara.
Australia too issued a similar alert on Wednesday.
"If there is a common platform against international terrorism, this information must be given to the concerned country. If the source for this kind of information is sound... it should not be given to the media," Erdogan told reporters late on Tuesday.
Suspect covers his face as he is
being brought to security court
A British Foreign Office spokeswoman said Britain conveyed information to countries where a threat occurred to reduce the risk of an attack.
Erdogan is also angry at Europe's footballing body UEFA for its decision to move three major European matches out of Turkey because of security concerns. He was expected to take up the matter by telephone with his British and Italian counterparts.
Short's body flown home
The body of British Consul General Roger Short, who was killed in the attacks, was flown to England early on Thursday in a military aircraft.
Short's flag-draped coffin was carried onto a Turkish military transport plane at Istanbul airport by soldiers acting as pall bearers, after a short prayer service.
The body of his assistant, Lisa Hallworth, who also died in the bombing, was also placed aboard with her family present.