Former Maoist rebels attacked vehicles, forced shops to close and blocked highways in Nepal to enforce a general strike called to protest the president.
The Maoists called the three-day strike in response to President Ram Baran Yadav, whom they accuse of acting unconstitutionally after he overturned the previous government's decision to fire the army chief.
Police spokesman Bigyanraj Sharma said 37 Maoist supporters had been arrested across the country but there were no reports of major violence.
Those detained were accused of vandalizing 16 vehicles that took to the streets and defied the general strike, which began Sunday, he said.
Political tensions have been high in Nepal since a Maoist-led government resigned in May amid the dispute with Yadav over the army chief's refusal to incorporate former Maoist rebels fighters into the military.
Since then, the former rebels have protested the president in the streets and in parliament.
The Maoists gave up their armed revolt in 2006 to join a peace process. They have since confined their fighters in UN-monitored camps and joined mainstream politics. They contested elections last year and won the most seats in parliament.
