In an email sent to the pro-Kurdish Firat news agency, the Kurdistan Freedom Falcons (TAK) said it carried out Tuesday's attack and warned: "It is only a beginning."

The group threatened to spread violence to urban areas, after a wave of deadly rebel attacks on army and police units in the southeast.

"Everywhere is a target," it said.

The bomb, which went off outside the administration offices of the capital, also injured at least 15 people.

Turkish officials say TAK is a front used by the Kurdistan Workers' Party (PKK), listed as a terrorist group by Ankara and much of the international community, especially when attacks claim civilian casualties.

The PKK has said TAK is a splinter group outside its control.