Former Turkish prime minister Ahmet Davutoglu on Friday said he would launch a "new political movement" after announcing his resignation from the ruling party in the latest challenge to President Recep Tayyip Erdogan from his former allies.
Davutoglu was the prime minister and chairman of the ruling Justice and Development Party (AKP) between 2014 and 2016 until relations soured with Erdogan and he was forced out.
There have been persistent rumors that he would establish his own party to rival the AKP.
"It is our historical responsibility and duty to the nation... to set up a new political movement," Davutoglu told reporters in Ankara.
Davutoglu had already served notice of his intentions earlier this year when he criticized the AKP's trajectory, especially after a controversial decision to annul the results of Istanbul's mayoral election when it was won by the opposition.
The opposition went on to win the re-run of the vote in Istanbul by an even wider margin, having also conquered the capital Ankara, both of which the AKP and its predecessors had held since 1994.
"I resign from the party where I have served with great honor, worked for years and given much effort to," Davutoglu said.
His resignation appears to have come before the party's decision earlier this month to send him to its disciplinary board for dismissal.
He described that decision as "very grave" and "not in harmony" with the AKP's founding principles.
"Unfortunately this decision on September 2 has passed in history as the day on which the AK Party has renounced its founding values and principles," he said.
Erdogan has seen an increasing number of defections from former allies in recent months, amid disquiet over the crackdown on political opponents following a failed coup in 2016.
Most notable among the defectors has been Ali Babacan, a former deputy prime minister and economy minister, who in July also announced plans for a new party after resigning from the AKP and citing the need for a "new vision" for Turkey.
Babacan was credited with overseeing Turkey's economic boom in the 2000s, having served as both economy minister and deputy prime minister between 2002, when the AKP first came to power, and 2015 when he left the government.