This comes as al-Qaeda claimed responsibility for the attacks, in a message to a Saudi newspaper.
The terrorist network also threatened the United States and Japan with “new operations”.
The US and Britain have also warned of further attacks, and many countries have increased security at sensitive sites.
“We have obtained very important clues and documents,” said Turkey’s Justice Minister Cemil Cicek.
“We have reached a certain point in our investigation, but this is a very complicated case. It has foreign ties and extensions.”
He has called on international cooperation to help Turkish police in their deliberations.
Seven people were detained on Friday in connection with the attacks, however no further information was given.
Turkish newspaper Hurriyet has also reported that police had identified the suicide bombers as two Turkish nationals.
Police have now issued a media blackout on the investigation, to prevent the publishing of any material that may prejudice the inquiry.
The death count has now reached 30, and at least 450 injured in the bomb attacks on the British Consulate and the HSBC bank in Istanbul. Five days earlier, car bomb attacks on two synagogues in the city killed 25.
Palestinian leader Yasser Arafat has condemned the bombings.
“The Palestinian people and I condemn the abject crimes which we reject, and we send our heartfelt condolences to the families of the victims of these terrorist acts and to the British government,” said Mr Arafat in a message to British Prime Minister Tony Blair.
Meanwhile European Union leaders have insisted that the blasts will not impact Turkey’s hopes of joining the EU.