The United States and Israel have issued fresh warnings to their citizens in Turkey citing threats which could target Istanbul and a coastal area popular with tourists.
"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," a message from the embassy on Saturday said.
The so-called "Emergency Message" urged citizens to exercise "extreme caution" while in touristic areas.
Turkish authorities have partially shut Taksim Square, at the end of Istiklal boulevard, the main high street in Istanbul, due to security concerns, Cumhuriyet newspaper and eye witnesses reported.
Istiklal was hit by a suicide bomber last month which killed four people, including three Israeli tourists and an Iranian citizen.
On Friday, Israeli media reported that the Counterterrorism Bureau was asking citizens to leave Turkey as soon as possible. Israel's previous warning said it was concerned about attacks by Islamic State.
Istanbul has been hit this year by two suicide bombings blamed on Islamic State, killing 16 foreign visitors.
Meanwhile, Ankara has seen two massive car bombs which combined killed 65 people, including military personal and civilians. Both attacks were claimed by the shadowy Kurdistan Freedom Falcons (TAK), an offshoot of the banned Kurdistan Workers' Party (PKK).
A two-year ceasefire between the state and the PKK broke down last year and the worst violence in two-decades has since flared up in the mostly-Kurdish south-east, leaving hundreds dead, including civilians.