(Adds HDP statement, details on detentions)
By Gulsen Solaker
ANKARA, Feb 9 (Reuters) - Turkish police detained leading members of several Kurdish and leftist parties on Friday, the co-leader of the main pro-Kurdish HDP party said, describing it as an attempt to hamper preparations for the annual HDP congress on Sunday.
Co-leader Serpil Kemalbay herself was among facing 17 suspects facing arrest over their opposition to Turkey's military offensive in neighbouring Syria, according to state-run Anadolu news agency.
Since the launch of the campaign in northwest Syria's Afrin nearly three weeks ago, authorities have said they would arrest those who criticise or oppose it. So far, some 600 people have been detained for protests or for social media posts against the military action.
Ankara prosecutors sought the arrests on accusations that the suspects sought to stir street protests and clashes under the guise of opposition to the Afrin offensive, Anadolu said.
The HDP, parliament's second-largest opposition party, is the only major political party to oppose the campaign - dubbed "Operation Olive Branch" - against the Kurdish YPG militia in Afrin.
"The aim of these illegal and arbitrary operations is to prevent our congress being held in a healthy way," Kemalbay said, promising that the party meeting would go ahead.
In Friday's raids, police detained the representatives and leaders of various left-wing and pro-Kurdish groups and political parties, Kemalbay said in a statement. She did not say how many were detained in total.
Kemalbay herself has not yet been detained and was still in the HDP headquarters in Ankara.
The HDP's other co-leader, Selahattin Demirtas, is in jail over alleged links to Kurdish militants and is among many leading members of the party imprisoned on similar charges, which they have denied.
The YPG is designated by Ankara as a terrorist group and an extension of the Kurdistan Workers Party (PKK), which has waged a three-decade-old insurgency on Turkish soil in which more than 40,000 people have been killed.
President Tayyip Erdogan said on Thursday Turkey would strip the word "Turkish" from the name of its main medical association after the group publicly opposed the campaign. (Additional reporting by Ali Kucukgocmen in Istanbul; writing by Daren Butler; editing by Dominic Evans/David Dolan and Mark Heinrich)
Our Standards: The Thomson Reuters Trust Principles.