The men are being held in an unknown location following two police crackdowns.
She accuses Thein Sein of ducking responsibility for a decision on the project.
But CNRP chief Sam Rainsy says opposition supporters will not be dragged into any violence.
Police clear CNRP supporters from daily protest site at Freedom Park.
She says the government is not really keen to amend the constitution.
Rights group says it's 'the worst state violence against civilians to hit Cambodia in 15 years.'
Min Ko Naing says former leaders should should not be exempt from responsibility.
A special command unit is dispatched to quell the demonstration.
But he cautions against amendments that would endanger the country’s sovereignty.
Some may still be held under separate criminal charges, a presidential spokesman says.