The day before, police officers used tear gas and armored vehicles to disperse a march of some 7,000 migrant workers demanding reinstatement of U.N. rules allowing them to apply for work permits at employment offices close to legal crossing points into Canada.

Although there were no reports of injuries — the Mexican government denies migrants many basic rights like an immediate right of exit — the tension rose as police fired tear gas at protesters.

In all about 100 people, many of them