Hundreds of former and would-be soldiers in Haiti refused government orders to disband and marched through the capital, many in mismatched uniforms. A United Nations spokesman said 40 to 50 of them were arrested.
UN spokeswoman Eliana Nabaa said they were arrested by Haitian police because they were carrying illegal weapons and acting as if they were part of the disbanded military.
A police spokesman could not be reached immediately for comment.
The ex-soldiers and their young recruits have been pressing President Michel Martelly to honour his campaign goal of restoring the armed forces, which was abolished in 1995 because of its abusive record.
Mr Martelly has said he wants to revive the military but that it must be done legally. His administration has repeatedly called for the lightly armed men to drop their weapons and clear out of 10 bases they have taken over since February.
But the government has taken little action to disband the group of men who have been parading about Haiti.
The march in Port-au-Prince was mostly peaceful but some people near the National Palace threw rocks at UN troops, who responded by firing tear gas. A few of the men in military uniforms carried handguns.