Sweep follows military questioning of election results with parliament due to sit this week.
Myanmar leader Aung San Suu Kyi and other senior figures from the governing party have been detained in an early morning raid, the spokesman for the governing National League for Democracy said on Monday.
The move comes after days of escalating tension between the civilian government and the powerful military that stirred fears of a coup in the aftermath of an election the army says was fraudulent.
Spokesman Myo Nyunt told Reuters by phone that Aung San Suu Kyi, President Win Myint and other leaders had been “taken” in the early hours of the morning.
“I want to tell our people not to respond rashly and I want them to act according to the law,” he said, adding he also expected to be detained.