US warns of 'Starbucks attack risk' in Turkey
The US embassy in Ankara said in a message to citizens that there are reports of a police investigation into a "terror cell" in Gaziantep.
The same city which is host to a large Syrian population was hit by a deadly suicide bombing on a wedding blamed on Islamic State group in August.
Syrian activists have also been murdered in the city by suspects linked to IS.
It said the information suggests the militants are "possibly targeting" shopping centres, Starbucks, the popular upscale Turkish restaurant chain Big Chef or other businesses frequented by Western customers.
"US citizens in Gaziantep are advised to exercise caution when patronising these sorts of businesses and to avoid them if possible," it said in the notice published late Wednesday.
A major city lying just 60 kilometres [37 miles] north of the Syrian border, Gaziantep has become a hub for Syrians fleeing the civil war in their country.
The Turkish authorities have acknowledged that IS militants had built up a presence in the city with the aim of staging attacks.
But the US embassy did not specify which group was suspected of planning to carry out the attacks.
Turkey has suffered a string of attacks in the last 12 months in Ankara, Istanbul and elsewhere blamed on Kurdish militants and IS.
In June, 47 people were killed in a triple suicide bombing and gun attack at Istanbul's Ataturk airport, with authorities pointing the finger at IS.
Fifty four people were killed in the 20 August suicide bombing on a Kurdish wedding in Gaziantep that President Recep Tayyip Erdogan said was carried out by a child bomber acting on the orders of IS.
Embassies are also on a high state of alert after a man wielding a knife tried to attack the Israeli embassy in Ankara on Wednesday.
Meanwhile the British embassy was closed last Friday for security reasons.
Separately, the official Anadolu news agency reported that 16 people were detained early Thursday on suspicion of membership of IS, in the latest of a series of raids in Istanbul.
It said that there was intelligence some could have been planning attacks in the city, and some had also taken part in the conflict in Syria.