They resigned in protest over the leadership of 35-year old Stefanos Kasselakis, a former banker who was picked as party leader in September after Syriza's heavy defeat in June's national election.

"SYRIZA is experiencing a dissolution crisis," the lawmakers said in a letter, accusing Kasselakis of contradictory positions and an ideological shift from leftist principles.

Syriza was catapulted to power at the height of Greece's debt crisis in 2015 but lost to the conservative New Democracy party in 2019 and again in June 2023, when it won just over 18% of the vote.

Recent opinion polls show Syriza trailing in third place, behind the Socialist PASOK party.

Earlier this month, two more lawmakers including former finance minister Euclid Tsakalotos had rebelled and the total number of those who have resigned now stands at 11, meaning Syriza now holds 36 of parliament's 300 seats.

The lawmakers who quit Syriza have the numbers to form a separate parliamentary group and could launch a new party ahead of European Parliament elections next year.

Kasselakis, a former Goldman Sachs associate who spent more than two decades in the United States and has almost no political experience, replaced former prime minister Alexis Tsipras, who resigned in June.

Some Syriza supporters were unhappy about Kasselakis' election, saying his profile did not fit the traditional Left and raising questions about his intentions. He said that knowing capitalism from the inside had turned him into a leftist.

The 20-year-old party has suffered splits in the past, especially after signing up to Greece's third bailout.

Political analysts expressed doubts about Syriza's future.

"It is very uncertain how Syriza can succeed under these circumstances," head of ALCO pollsters Costas Panagopoulos told Reuters.

(Reporting by Renee Maltezou; Editing by Gareth Jones)