The Kurdistan Freedom Falcons (TAK) said Sunday's attack at a police patrol in downtown Istanbul was an act of revenge "against the police force of Turkish fascism" and was organised and carried out by a member of its command.

TAK is a shadowy group that upholds Kurdish rebel leader Abdullah Ocalan as its "chairman" but says it is not linked to his Kurdistan Workers' Party (PKK), which has led a bloody 26-year campaign for self-rule in the Kurdish-majority southeast.

The PKK says TAK is a splinter group outside its control, but Ankara believes it is a front for PKK attacks in urban centres that result in civilian casualties.

The authorities have identified the suicide bomber as a PKK militant.

The PKK leadership however denied responsibility for the attack and extended a truce, first declared in August, until general elections next summer, saying it wanted to push for a peaceful settlement of the Kurdish conflict.

In its statement Thursday, TAK made it clear it disagreed with the truce and would not observe it.

"We have seen no development that would justify the silencing of TAK weapons and we maintain our position on that," it said.

It warned "all forces" who oppress the Kurds that "sooner or later they will become the target of TAK's suicide commandos."

In Sunday's attack, the bomber blew himself up as he attempted to get on a police bus at Istanbul's busiest spot, Taksim Square, wounding 15 officers and 17 civilians.

Most recently, TAK claimed responsibility for a roadside bomb that hit a bus carrying army personnel in Istanbul in June, killing five soldiers and a teenage girl.