Officials have accused the separatist Kurdistan Workers' Party (PKK), which takes refuge in neighbouring northern Iraq, after two blasts killed 17 people, five of them children, in a crowded Istanbul street Sunday night.

Witnesses told police to seek a swarthy man about 20 to 25 years old, 170cm (5ft 8in) tall and wearing a green t-shirt who was in the Gungoren neighbourhood and who they said could have planted the devices there.

"The police, who have established a description of the terrorist... are working on the presumption that he came alone from the Qandil mountains," the daily Vatan reported, referring to the mountains in northern Iraq where the PKK has its main stronghold.

Turkish fighter jets targeted the region Tuesday, bombing a cave the PKK used as a base, destroying the hideout and killing most of the 30 to 40 militants spotted there, the army said.

A second PKK target, in the Zap region along the Turkish border, was also bombed, the statement said, but gave no further details.

Turkish warplanes have been bombing PKK positions in northern Iraq since December, backed by US intelligence on rebel movements in the region.

The PKK, listed as a terrorist group by Ankara and much of the international community, has carried out bomb attacks against civilians in the past, but the group has denied responsibility for Sunday's blasts.

On Monday, Prime Minister Recep Tayyip Erdogan all but named the PKK as the perpetrator, describing the two explosions as "the cost" of the intensified military crackdown against the rebels in Turkey and northern Iraq.

He said Tuesday that police would announce their final conclusion once the investigation is over.

Interior Minister Besir Atalay said investigators had established that TNT was used in the attack and were examining pieces of mobile telephones found at the site, apparently used to detonate the devices.

Vatan said the second bomb, which exploded about 10 minutes after the first had drawn a crowd of onlookers, was a timed device to avoid the police scramblers that would have been activated to render a second detonation by cellphone impossible.

All 17 victims perished in the second explosion.

The attack heightened tensions as the Constitutional Court began deliberating Monday on whether to outlaw Erdogan's Islamist-rooted Justice and Development Party (AKP) for undermining Turkey's secular system.

It coincided with another high-profile case, against the shadowy "Ergenekon" nationalist group, which is alleged to have organised attacks and plotted assassinations to foment political turmoil and pave the way for a military coup against Erdogan's government.

Late Monday, the BBC broadcast an interview with Murat Karayilan, leader of the PKK's military wing, which it said it had obtained several weeks ago. In its translation, the broadcaster said Karayilan had raised the possibility of a campaign against economic and military targets in Turkish cities.

The PKK took up arms for Kurdish self-rule in the southeast in 1984, sparking a conflict that has claimed more than 37,000 lives.