Supporters of ousted Myanmar leader Aung San Suu Kyi clashed with police on Friday as hundreds of thousands joined nationwide pro-democracy demonstrations in defiance of the military junta’s call to halt mass gatherings.

The United Nations human rights office said more than 350 people, including officials, activists and monks, have been arrested in Myanmar since the Feb 1 coup, including some who face criminal charges on “dubious grounds”.

The UN rights investigator for Myanmar told a special session of the Human Rights Council in Geneva that there were “growing reports, photographic evidence” that security forces have used live ammunition against protesters, in violation of international law...