A Turkish prosecutor ordered the detention of the head of the Turkish Medical Association (TTB) and 10 other leaders of the doctors' union on Tuesday, after the body criticized Turkey's military operation in north Syria.
The prosecutor said police in Ankara started legal proceedings on Tuesday morning and search-and-detention operations were going on in eight provinces.
Turkish authorities have cracked down on any expression of dissent over the air and ground offensive against the Syrian Kurdish YPG militia in Syria's Afrin region. More than 300 people have been detained for social media posts criticizing the campaign since it began 10 days ago.
TTB head Rasit Tukel and other members of the board had been detained, opposition CHP lawmaker Ali Seker said on Twitter.
The association's lawyer Ziynet Ozcelik said they faced accusations of "propaganda in support of a terrorist organization, and provoking the public". Ozcelik said it was the first time in the association's history that all its executive members had been ordered detained.
The Turkish Medical Association denounced the cross-border operation into Syria's Afrin last week, saying "No to war, peace immediately".
President Tayyip Erdogan accused the union of treason on Sunday. "Believe me, they are not intellectuals at all, they are a gang of slaves. They are the servants of imperialism," he told AK Party members in the northern province of Amasya.
"This 'No to war' cry by this mob ... is nothing other than the outburst of the betrayal in their souls ... This is real filth, this is the honorless stance that should be said 'no' to," Erdogan said.