Anatolia news agency reported that eight people, suspected of involvement in the massive bombings on 15 and 20 November which left 62 people dead, had been detained in Konya earlier this month.
Police discovered igniters and other devices used in the making of bombs, as well as sketches and other unspecified documents in the house where the suspects were rounded up.
Among the eight suspects were three men believed to be senior members of Turkish groupings, linked to the al-Qaida network, which has claimed responsibility for the Istanbul blasts along with a Turkish group, the Islamist Great Eastern Raiders Front.
Following the testimony of one of the men, police conducted a second search in the house and found five Kalashnikov rifles and 1000 bullets in a secret compound, Anatolia said.
It did not say when the operations took place.
The report coincided with the seizure of a massive amount of bomb-making equipment in Istanbul, reported by the media on Tuesday.
The press said police had seized enough material to build five truck bombs similar to those which rocked the city last month.
Officials have said they will make a statement on the issue
In a document leaked to the media this week, the police warned of possible new attacks during the New Year holidays, but officials sought to play down the threat.
The memo said police had intelligence that several people from a group of militants planning a new "large scale" attack in Turkey, had crossed into the country from Syria.
The document, dated 22 December, urges security forces to be vigilant over Christmas and mentions Western interests, particularly those of the United States and Israel, as well as the luxury Akmerkez shopping mall in Istanbul as possible targets.
Officials, however, said on Wednesday they had no information about a specific threat, but confirmed that security had been tightened before the New Year holidays.