ISTANBUL (Reuters) - Turkish police have detained 48 suspected Islamic State members who were preparing to launch an attack, an Istanbul police spokesman and state-run Anadolu news agency said on Saturday.

Police raided six addresses in three districts of Istanbul late on Friday, and detained 31 foreign nationals, the police spokesman said in a statement.

Seventeen more foreign nationals who were also preparing to launch an attack were detained in raids across the capital Ankara, Anadolu said, without specifying when the operation was carried out.

Officers seized digital material and documents during the operations, Anadolu said.

Turkey has been a partner in the U.S-led coalition against Islamic State fighters.

Turkish police stepped up operations against Islamic State suspects at the end of last year before the first anniversary of a New Year gun attack on a nightclub in Istanbul in which 39 people were killed.

Islamic State claimed responsibility for that shooting, one of a series of attacks believed to have been carried out by the jihadists in Turkey in recent years.