A leader of the country's biggest doctors' assocation appeared before police for questioning Wednesday in connection with the walkout by trainee doctors protesting the government's decision to hike the medical school quota.

The questioning of Joo Soo-ho, the chief spokesperson of the Korea Medical Association, came as thousands of intern and resident doctors have stayed off the jobs at general hospitals nationwide for the 16th day in protest of the plan to raise the quota by 2,000 beginning next year from the current 3,058.

Joo is the first to face police questioning among the five current and former KMA executives against whom the government filed a criminal complaint on charges of instigating and conniving in the trainee doctors' collective action.

They were also accused of violations of the Medical Service Act and obstructing the operations of the training hospitals affected by the walkout.

Before entering the Seoul Metropolitan Police Agency's building in Seoul, Joo squarely denied the charges.

"Literally, I have nothing to hide, nor reasons to hide," he said, adding that the walkout was inevitable given the "murderously" cheap medical reimbursement from the national health care insurance.

He claimed that the doctors' collective action was "voluntary" and called on the government to engage in dialogue with protesting doctors for compromise.

Through next week, police plan to question the rest of the accused KMA officials, including former chief Roh Hwan-kyu on Saturday and current chief Kim Taek-woo next Tuesday.

An overseas travel ban has been issued on all five of the accused KMA officials.