The U.N.'s top human rights official is urging Thailand's military government to ease limits on free speech, especially those restricting debate over a proposed constitution that faces a referendum in August.

U.N. High Commissioner for Human Rights Zeid Ra'ad Al Hussein also expressed concern in a statement Friday about the military's expanding role in policy-making and law enforcement.

Thailand has been ruled by a military junta since a May 2014 coup ousted an elected government. The junta uses arbitrary detention to punish critics, and recently announced strict limits on public expressions of criticism or support of the draft constitution, a move directed chiefly against the charter's opponents.