A migrant caravan of over 400 people, including many children, started for the U.S. from the southern Mexican city of Tapachula on Saturday, Sept 4, only days after security and migration officials dispersed another similar group.

People from El Salvador, Honduras, Guatemala, Haiti, and Venezuela make up the majority of the group.

A Reuters witness reported that the caravan left around 7:30 a.m. local time from a park in Tapachula where they had been staying, despite security officers’ attempts to persuade them not to go.

It’s the fourth such group to set out in the last week, despite the presence of a large number of Mexican national guards intent on stopping the asylum seekers.

Police have used excessive force against the migrants, according to activists and UN officials accompanying them. Two migration agents have been placed on leave after hitting a traveler.

Despite this, the administration has stated that it will continue to prevent U.S.-bound migrants from passing through Mexico.

According to the AFP, President Andres Manuel Lopez Obrador said he would send U.S. President Joe Biden a letter reiterating his proposal for the U.S. to grant work visas to Central Americans and Mexicans, as well as address the poverty and violence that are among the issues fueling these migratory flows, according to the AFP.

Since Biden took office in the White House, Mexico has seen an uptick in undocumented migrants going north.

The Mexican government claims it has deployed over 27,000 security officers to its southern and northern borders to stem the influx.