Tourists in the Turkish city of Istanbul are on high alert after a female suicide bomber blew herself up in a crowded area.

One police officer was killed during the incident, while another was left with serious injuries.

The woman walked into a police station in the historic area of Sultanahmet, close to the Blue Mosque and Hagia Sophia.

Both are among the most popular tourist attractions in the city.

No group has claimed responsibility for the attack, which was the second in less than a week.

Last Thursday, a man threw grenades and fired a weapon at police near the prime minister’s office, but no-one was hurt.

The UK Foreign & Commonwealth Office warned Britons in the country there is a high threat from terrorism in Turkey.

FCO advice warned: “On January 6th 2015, a Turkish police building in Istanbul’s main tourist district, Sultanahmet was targeted by a suicide bomber.

“The assailant died in the attack along with a Turkish police officer. If you’re in this area you should follow the advice of the local authorities.”