At least 200 demonstrators blocked a major commercial bridge between Mexico and Texas to protest the disappearance of dozens of people in the border city of Nuevo Laredo, snarling traffic in both directions for most of Monday.
The protest began around 9:30 a.m. at the bridge, which is used exclusively by cargo trucks traveling between Tamaulipas state and Laredo, Texas, and was still going on as of late afternoon.
Thousands of trucks make the crossing each day, and long lines of tractor-trailers backed up along the highway.
Demonstrators were protesting what they consider a weak response by authorities to 43 complaints filed with prosecutors over disappearances in Nuevo Laredo.
"We are demanding justice," said Estela Gonzalez, who lodged a complaint about a missing nephew-in-law. "Alive or dead or however they may be, we want to know what happened to them."
Nuevo Laredo's acting mayor, Rafael Pedraza Dominguez, went to the bridge in the afternoon to try to persuade the protesters to leave, promising to engage in talks with them.
But they ignored his pleas and vowed to maintain the roadblock.
"What we want is a solution, and if (the missing) have already been harmed, well, what happened to their bodies?" Gonzalez said.
Nuevo Laredo is a key smuggling corridor for rival drug gangs, and the city has been experiencing a wave of violence.
In March, four members of a family were killed in the crossfire between Mexican marines and gang members. The following month federal prosecutors issued a report faulting officers for the deaths.