Iraq's top court said on Tuesday it was dismissing parliament speaker Mohamed al-Halbussi, an influential Sunni Muslim politician, after a lawmaker's complaint over the alleged "falsification" of a document.

Halbussi has been the highest ranking Sunni official since he first became speaker in 2018 of parliament -- elected with the support of Iraq's powerful pro-Iran parties.

He was reelected as speaker in January 2022 following early parliamentary elections the previous October.

"The Federal Supreme Court ends the mandate of the President of Parliament" Halbussi, the court said in a short online statement.

It added that it had also ended the mandate of another Sunni lawmaker, Laith al-Duleimi.

The court began reviewing a case filed against him in February after Duleimi accused him of forging a resignation letter, saying the speaker had changed the date on an older document to force him out of parliament.

Iraq's 329-member parliament is dominated by a coalition of pro-Iran Shiite parties.

Halbussi led a sizeable Sunni bloc, with his Taqadom party's 37 members in parliament, until he faced growing unease within Iraq's Sunni political sphere in recent months.

Duleimi, who was an MP for Taqadom, slammed his ousting from parliament in January as "illegal".

Halbussi reacted to Tuesday's decision, which cannot be appealed, during a parliamentary session, condemning it as "a strange verdict".

"Unfortunately, some seek to destabilise the country," he charged.

"We are surprised by the promulgation of such decisions. We are surprised by the lack of respect for the constitution," he added, pledging to tackle the matter and adjourning the session.

Under a power-sharing system adopted in Iraq in the aftermath of the 2003 US-led invasion, political positions are divided between Iraq's ethnic and confessional communities.

In the top positions, the prime minister role, currently held by Mohammed Shia al-Sudani, always goes to a Shiite Muslim, the presidency to a Kurd and speaker of parliament to a Sunni Muslim.

Halbussi, the former governor of the Sunni-majority western Al-Anbar province, is known for his rapid ascent in Iraqi politics and being a key interlocutor for many Western and Arab dignitaries.

First Deputy Speaker Mohsen al-Mandalawi will assume Halbussi's role until a new speaker is elected, according to a former MP.