Brian Cobb, an American doctor, was reportedly detained Wednesday after he appeared on a private television channel the day before saying he and others were brutally assaulted by the security forces.
On Tuesday, Cobb had told Kantipur television channel that truncheon-wielding policemen swooped down on him and other people and started hitting them indiscriminately.
The doctor also told the channel he saw a man's eye being gouged out by the security forces. Cobb left Nepal Thursday, the daily said.
It also said the visa of a German doctor, identified only as Angel, who had been treating injured demonstrators, was cancelled. However, it was not known immediately if he was still in Nepal.
Since the royalist government imposed daytime curfew in Kathmandu valley from Saturday and authorised the security forces to shoot at sight, human rights organisations have been expressing dismay at the excessive use of force to stop protests.
In Thamel, the tourist hub in the capital, police swooped down on a small group of people Tuesday when they stood at a prominent square, holding improvised placards asking for the restoration of democracy and peace.
Nine tourists, including citizens from Germany, Britain, Israel and Russia, were taken to the police station and released after questioning.
On Thursday, the second day in a row, the security forces broke up a peaceful sit-in in the capital by nearly 50 leading international NGOs, demanding peace to be able to conduct development work. A local media agency, Nepalnews.com, said the continuing repression showed the zero tolerance policy of the royalist government.