Turkey accuses outlawed Kurdistan Workers' Party (PKK) militants of executing 13 police officers and security personnel, whom they had abducted in Turkey and held hostage in a cave in northern Iraq.

But the PKK, which is listed as a terrorist organisation by Turkey and its Western allies, said the 13 were killed by Turkish bombs dropped during a rescue operation that Ankara launched last week.

The failed rescue attempt has piled political pressure on Erdogan, who has ruled Turkey as prime minister and president since 2003.

Kemal Kilicdaroglu, leader of the main opposition Republican People's Party (CHP), said Tuesday in parliament it was "Erdogan who is responsible for our 13 martyrs".

"You launched an operation but all the hostages died," Kilicdaroglu said.

His comments infuriated Erdogan, whose lawyers are now seeking 500,000 Turkish liras ($72,000, 60,000 euros) in "moral damages", the Anadolu state news agency reported.

The pro-Kurdish Peoples' Democratic Party (HDP), parliament's second-largest opposition group, also criticised Erdogan for the failed operation, arguing that negotiations would have been more effective.

And Ahmet Davutoglu, a former prime minister who quit Erdogan's ruling party last year, called the operation a "failure" as well.

"What's important in rescue operations is to save lives, not a political show," he told a party congress.

But Erdogan's right-wing allies, the Nationalist Movement Party (MHP), threw their support behind the government.

"Turkey is a rising power which fought in (northern Iraq) not only against the PKK but also against strategic threats," MHP leader Devlet Bahceli tweeted.

The Turkish army regularly conducts cross-border operations and air strikes on PKK bases in northern Iraq.

On Wednesday, Erdogan said that more than 12,900 Kurdish militants -- 6,000 at home and 6,900 abroad -- had been killed since a ceasefire with the PKK broke down in July 2015.

The PKK has fought an insurgency against the Turkish state since 1984 that is believed to have left more than 40,000 dead.

Turkey's botched rescue attempt also caused a diplomatic spat with the United States, which initially said it was waiting for official confirmation before blaming the deaths on the PKK.

Washington did blame the group later however after Erdogan accused the US of siding with "terrorists".