Turkish authorities have tightened security across the port city of Istanbul as the country remains on high alert after a spate of deadly bomb attacks, media reports say.
CNN Turk and the Hurriyet newspaper reported on Thursday that police were individually checking passengers before allowing them to ride the Marmaray railway that runs under the Bosphorus Strait linking Istanbul’s European and Asian sides.
Earlier this month, Prime Minister Binali Yildirim said heavily armed special forces had been deployed on the Marmaray, the airport and train stations in Istanbul.
Photos posted on social media on Wednesday showed Turkish special forces patrolling Istanbul's Istiklal street, a popular shopping area for locals and tourists.
The increased security measures came one day after France closed its embassy in the Turkish capital, Ankara, and its consulate in Istanbul until further notice due to security concerns.
France also cancelled planned events in its mission in Turkey to mark French National Day.
The consulate general in Istanbul said earlier that it had received information warning of a "serious threat against plans for the celebration of the July 14 national holiday in Turkey”.
Turkey has been rocked by a series of bombings since the beginning of this year, blamed on both Daesh terrorists and Kurdish militants.
The latest gun and bomb attack took place on June 28, when three bombers opened fire outside Istanbul's international airport. Later, two of the assailants got inside and set off their explosives while the third blew himself up at the entrance.
The Ataturk airport incident, which was blamed on Daesh, killed nearly 50 people, including foreign nationals, and left more than 200 others injured.