The reports said the police had seized nearly 50 pounds of plastic explosives with detonation systems attached, as well as six laptop computers and other evidence. Twelve people were detained during the operation — two Chechens, two Azeris and eight Turks.

The evidence was gathered during a raid on two terrorist cells, one in Istanbul and one in Corlu, a district of Tekirdag on the Sea of Marmara. Forensic analysis of the computers’ contents and other documents, officials said, revealed preparations for bomb attacks on the embassy, the private Rahmi M. Koc Museum and a synagogue in the Balat district of Istanbul.

Photographs, floor plans and other information were found concerning those targets and the residences and offices of two well-known Turks.