ANKARA, Turkey (AP) — A former Turkish deputy prime minister and key figure in President Recep Tayyip Erdogan’s ruling party has resigned, signaling plans to form a rival political party.

Ali Babacan, who had also served as economy and foreign affairs minister in various Erdogan governments, on Monday announced his resignation from the ruling Justice and Development Party, citing deep differences “in principles, values and ideas.”

Babacan was rumored to have been planning to form a splinter party along with former President Abdullah Gul and others said to be disgruntled with Erdogan’s increasingly authoritarian rule. Former Prime Minister Ahmet Davutoglu is also reported to be planning to establish a separate party.

Babacan said: “The need to start a new effort for Turkey’s present and future has become inevitable.”