At least 17 people have been killed and 150 hurt by two bombs in a residential area of the Turkish city of Istanbul.
The first bomb was planted in a rubbish bin in the Gungoren area. It caused crowds to gather before a second, larger device detonated.
No group has claimed responsibility, but security services said the attack bore the hallmarks of Kurdish rebels.
It came hours before the constitutional court began deliberations over whether to ban the ruling AK Party.
The AKP forms the country's government and won a resounding victory in elections just last year, but Turkey's secular elite accuses the party of seeking to impose an Islamic agenda - a charge it denies.
The BBC's Sarah Rainsford, in Istanbul, says the chances are that the court will close down the AK Party, casting doubt over Turkey's political future, its international relations and relations with the European Union.
The long-running court battle with the AKP has been overshadowed by the bloodshed in Istanbul.
The death toll, which stood at 16 overnight, rose to 17 on Monday after one injured person died in hospital, the country's health minister said.
Seven more people remain seriously injured, Recep Akdag told the country's Anatolia news agency.
Some Turkish newspapers reported on Monday that three people had been arrested near the scene of the bombings, but there was no confirmation of this by the police.
Turkey's President Abdullah Gul said the attack on Istanbul showed "the ruthlessness of terrorism", while Prime Minister Recep Tayyip Erdogan said such attacks only strengthened Turkey's determination in its fight against terrorism.
The blasts occurred about 10 minutes apart around 2200 local time (1900 GMT) on a busy pedestrian street.
There were scenes of panic, with people covered in blood as they tried to run from the scene. TV footage showed many victims lying on the street and being carried to ambulances in blankets.
About 1,000 were said to be in the area at the time on a warm summer evening.
"The first explosion was not very strong," Huseyin Senturk, the owner of a nearby shoe shop, told the Associated Press.
"Several people came to see what was going on. That's when the second explosion occurred and it injured many onlookers."
Police in Istanbul quickly linked the bombings to the Kurdish separatist group, the Kurdistan Workers Party (PKK).
The group has bombed Turkish civilians before, and may be seeking revenge for recent operations by the Turkish military against its bases.
Istanbul Governor Muammer Guler said "there appears to be a link" with the PKK. He said the authorities were trying to confirm it.
But the PKK leader Zubeyir Aydar was quoted by pro-Kurdish news agency Firat denying any involvement.
"The Kurdish freedom movement has nothing to do with this event, this cannot be linked to the PKK," he was quoted as saying.
Suggestions that Islamist groups planned the attack were played down, as previous attacks by Islamists have targeted foreign consulates or businesses in Istanbul.
In November 2003, more than 60 people were killed by a series of suicide bombings in Istanbul, which the authorities linked to al-Qaeda.