US warns its citizens of 'credible threats' in Turkey

The United States Embassy in Turkey has warned American citizens of "credible threats" to tourist areas in Istanbul and the resort city of Antalya, a day after Israel spoke of "imminent risks" of attacks.

"The US Mission in Turkey would like to inform US citizens that there are credible threats to tourist areas, in particular to public squares and docks in Istanbul and Antalya," read the emergency travel warning published on Saturday on its official website.

"Please exercise extreme caution if you are in the vicinity of such areas."

The warning came three weeks after a suicide bomber struck the popular shopping thoroughfare of Istiklal Caddesi in the heart of Istanbul, killing four people and injuring dozens, in an attack which authorities blamed on the Islamic State group.

A series of attacks in Ankara and Istanbul that have been blamed on Kurdish militants or jihadists have put the country on high alert and seen foreign embassies put its residents on guard.

On Friday night Israel reissued a warning to its citizens to avoid Turkey or "leave as soon as possible".

"Following a situational assessment, we are reiterating and sharpening the high level of threat in Turkey," Israel's counter-terrorism bureau said.

"There are immediate risks of attacks being carried out in the country, and we stress the threat applies to all tourism sites in Turkey."