Brussels  - European Union officials on Monday condemned as "despicable" the overnight double bombing in a crowded Istanbul street which left at least 17 people dead.

"I condemn in the strongest possible terms the despicable bombing attack that took many innocent lives and injured dozens of people in Istanbul yesterday (Sunday) evening," Javier Solana, the EU's high representative for its common foreign policy, said in a statement.

"I express my deepest condolences and my heartfelt sympathy to the families of the victims and to the Turkish government ... In these difficult moments, Turkey can count on the support of the European Union," he said.

The double bomb attack struck a pedestrian street in the Gungoren district of Istanbul late on Sunday evening, leaving at least 17 dead and over 150 injured.

The attack was "clearly designed to kill as many people as possible," the EU's executive body, the European Commission, said in a statement.

The Brussels-based body "condemns in the strongest possible terms the hideous bomb attack" and "expresses its solidarity with the Turkish people in the fight against terrorism and sends its condolences to the families of the victims," the statement said.

Police on Monday morning were searching for clues as to the perpetrators, with Kurdish separatists and Islamist extremists among the suspects.

Turkey is a current candidate for EU membership, but its entry into the 27-member union is opposed by several members including France and Germany.

On Monday morning Turkey's Constitutional Court began deliberating whether it should close the country's ruling political party for allegedly breaching the strictly secular constitution. (dpa)