ANKARA (Reuters) - Turkish authorities detained nine officials from the country's main pro-Kurdish opposition party on Saturday, a party official said, a day after the party's leaders were formally arrested.

The nine officials included the provincial and district heads of the pro-Kurdish opposition Peoples' Democratic Party (HDP) in the southeastern province of Adana, the official said.

HDP co-leaders Selahattin Demirtas and Figen Yuksekdag were arrested on Friday as part of a terrorism investigation, prompting strong international condemnation of a widening crackdown on dissent under President Tayyip Erdogan.

(Reporting by Gulsen Solaker; Writing by Tuvan Gumrukcu; Editing by Catherine Evans)