Turkey's president has approved amendments to the constitution that pave the way for the trials of some 138 legislators, including several pro-Kurdish lawmakers who face terror-related charges.

The state-run Anadolu Agency said Recep Tayyip Erdogan on Tuesday ratified the changes which were put forward by the ruling party and finally approved by parliament last month after heated debates.

Erdogan has accused the pro-Kurdish People's Democratic Party, or HDP, of being an arm of the outlawed Kurdish PKK rebel group.

The Turkish state has been locked in renewed conflict with Kurdish fighters since last summer when a 2 ½-year truce with the Kurdistan Workers' Party, or PKK, collapsed. Kurdish rebels have set up trenches, barricades and explosives to keep the authorities out of areas where they want autonomy.