Parliament hastily passed the bill, backed by the ruling Justice and Development Party (AKP), in the early hours of Friday.

The new law requires the prime minister to authorise any court cases against intelligence agents for their work on missions controlled directly by the premier.

The bill was passed in the wake of a case involving several members of Turkey's National Intelligence Organisation (MIT) having contacts with the banned Kurdistan Workers Party (PKK).

Prosecutors had summoned several MIT members, including its current chief Hakan Fidan and former head Emre Taner, for questioning over the contacts.

Prosecutors alleged that the MIT members had exceeded their authority when they broached the topic of a political settlement with the rebels, who have been fighting the government for nearly 30 years.

When the agents refused to show up for the questioning the prosecutor who issued the summons, Sadrettin Sarikaya, ordered the agents' arrest. He was then pulled from the case.

MIT chief Fidan had secret talks with representatives of the PKK in 2010 in Oslo.

Recordings of the Oslo talks between MIT and the Kurdish rebels were leaked in the media last year, sparking outrage among opposition politicians.

They accused the ruling AKP party of having abandoned the official position of no contact with the PKK.

The PKK took up arms in southeastern Turkey in 1984, sparking a conflict that has claimed some 45,000 lives. It is labelled a terrorist outfit by Ankara and much of the international community.

But many specialists argue that there is no military solution to the conflict and that political talks are required.