A new group of migrants bound for the US has set off from El Salvador, following thousands of other Central Americans fleeing poverty and violence who have taken similar journeys in recent weeks.
The group of more than 300 Salvadorans left the capital San Salvador on Sunday. A larger group of mostly Hondurans, estimated to number at least 3,500, left that country in mid-October and is now in southern Mexico. That group has become a key issue in US midterm elections.
A third group has been moving through Guatemala, at one point numbering more than 1,000 before beginning to fragment. Hundreds broke through a Guatemala border gate in Tecun Umanand on Sunday afternoon were on the bridge into Mexico.
Migrants say joining a large group offers a measure of protection against police officers and bandits.
Donald Trump and his fellow Republicans have sought to make immigration a major issue ahead of the 6 November elections, in which the party is battling to keep control of Congress.
Homeland security secretary Kirstjen Nielsen said on Fox News Sunday Trump was determined to use every authority he had to stop immigrants crossing the border illegally.