ANKARA (Reuters) - Three suspected Islamic State members, one a Briton and two Pakistani, were arrested last week in Istanbul following raids carried out by Turkish security forces, Dogan news agency reported on Tuesday.

The three men were placed under arrest by a Turkish court after being seized in separate raids on Dec. 24 and 25, Dogan said, citing police and judicial sources. Another Pakistani man was released by the court.

None of the men has been named.

Last month Turkish authorities picked up another Briton saying he was an associate of Islamic State leader "Jihadi John", who is thought to have been killed in a coalition air-strike.

Turkey has stepped up its efforts to tackle the militants after the group was blamed for a double suicide attack in Ankara in October that killed 100.

Turkey has a 900 km (550 mile) border with neighboring Syria, some of it controlled by Islamic State, and has become a transit route for would-be jihadists.

(Reporting by Ece Toksabay and Jonny Hogg; Editing by Ruth Pitchford)