More terror attacks on cities in Turkey may be "imminent", the British Government has warned.
Several people have been charged in connection with the attacks
Firming up travel advice to the region, the Foreign Office said new information suggested Istanbul and Ankara could be likely targets.
Nine people have been charged in connection with last week's double suicide bombings in Istanbul.
Meanwhile, a Turkish woman injured in the bombing of the British Consulate has died of her injuries in hospital.
Hulya Donmez, 27, the fiancee of Briton Graham Carter, had been on life support after suffering serious head and chest injuries in the blast.
The Foreign Office has already warned against all non-essential travel to Turkey.
But revising its guidance on Tuesday, it said: "We have information to suggest that further attacks may be imminent in Istanbul and Ankara.
"We urge you to be vigilant in all parts of the country and especially in the vicinity of potential terrorist targets."
It suggests sites symbolising the political, religious and economic values of western countries including the UK are particularly at risk, though Turkish buildings have also been targeted in the past.
The BBC's security correspondent Frank Gardner said the new warning indicated progress had been made in the hunt for the bombers.
He told BBC News: "I think it's fair to assume this is intelligence-led, that the joint investigation with the Turkish authorities into the bombings has yielded clues, that this is not the end of it, that this whole wave of bombings is not yet completed."
Groups apparently connected to al-Qaeda say they carried out last Thursday's bombings, in which at least 28 people died.
Three others detained after the attacks have since been freed.
'Truth and falsehood'
The morning sermon read in Turkish mosques on Tuesday had a strong anti-terrorist message, underlining the Islamic message of love and tolerance and condemning terrorism, whatever its motivation.
The sermon was issued by the state-run Religious Affairs Directorate at the start of the three-day religious holiday marking the end of the fasting month of Ramadan.
Prime Minister Recep Tayyip Erdogan, in a televised national address on the eve of the holiday, also urged people to resist terrorism.
"This is a war between justice and cruelty, good and bad, and truth and falsehood," he said.
"It is our right to expect every sensible person to stand by justice, good, and truth in this war."
Part of the British consulate was destroyed in the attack
The suspects who appeared in court were among 18 detained after the twin attacks on the British consulate and a branch of the London-based HSBC bank.
Anatolia news agency said they were accused of "belonging to, aiding and abetting an illegal organisation".
Authorities had earlier charged five people with "attempting to overthrow the constitutional structure", for their alleged roles in the twin synagogue bombings in Istanbul five days earlier.
A sixth person was charged with "helping illegal
The governor of Istanbul said police had gathered "very important clues" on who carried out the bombing outside the British consulate.
Istanbul governor Muammer Guler said police had identified the "culprits" of the attack, but declined to name the suspected bomber.
However, a Turkish newspaper said DNA tests had identified the driver of the van, which had been packed with explosives, as a Turkish man named Feridun Ugurlu.
Police, who have accused the media of hampering the investigation by leaking information, have refused to confirm the report.
Feridun Ugurlu had previously been named as an accomplice in the synagogue attacks.
At least 23 people died in those attacks and hundreds were injured.
Turkish officials have said the bombers were Turkish nationals with links to radical Islamic groups.
Full travel advice for Turkey is available on the FCO website or by calling 0870 606 0290.