ANKARA (Reuters) - Turkey’s pro-Kurdish Peoples’ Democratic Party (HDP) said on Sunday it would take part in a parliamentary commission charged with drafting a new constitution and would challenge the ruling AK Party’s plans for a strong executive presidency.

The AK Party has broad cross-party support for overhauling Turkey’s constitution, which dates back to an era of military coups, but there are wide divergences over what a new charter should look like.

President Tayyip Erdogan and the AK Party he founded more than a decade ago want the head of state, who currently has a largely ceremonial role, to wield much greater political powers.

But the opposition parties want to focus on improving minority rights and democratic freedoms and fear Erdogan is becoming too authoritarian, a charge he rejects.

Turkey’s Parliamentary Speaker Ismail Kahraman of the AK Party has invited the opposition parties in parliament to join the commission but the HDP had not previously said whether it would attend. Deeply suspicious of Erdogan and the government, some HDP lawmakers had called for a boycott.

“We will be on the constitutional reconciliation commission. But we have serious differences with the AK Party in many fields such as freedom, equality and justice,” HDP co-chair Selahattin Demirtas told a party congress to loud cheers.

“Despite these differences we will meet them without any prejudice and will seek reconciliation for peace,” he told delegates, including representatives of European socialist parties, at the congress, held under tight security.

Relations between the AK Party government and the HDP have soured considerably since a surge in violent clashes between Turkish security forces and militants of the outlawed Kurdistan Workers Party (PKK) in Turkey’s mainly Kurdish southeast.

The HDP wants any new Turkish constitution to decentralise power away from Ankara to the regions.

“We will present our proposal for the constitution in which local authorities are more powerful,” HDP Izmir Deputy Ertugrul Kurkcu told Reuters. “We will never discuss a ‘one man administration’ because we want a parliamentarian republican system based upon powerful local authorities.”

The Islamist-rooted AK Party lost its single-party majority in an election last June but, after coalition talks failed, it swept back to power in a snap poll, capturing nearly 50 percent of the vote.

However, the ruling party still needs the support of 14 opposition lawmakers to be able to put a new constitution to a popular referendum and it needs 50 more votes to push a final deal through a bitterly polarised parliament.