The organizer of a migrant caravan from Honduras was detained in Guatemala on Tuesday.
The US government said if the flow of northbound migrants was not stopped, they will withdraw aid from both countries and El Salvador.
Up to 3,000 migrants crossed from Honduras into Guatemala on a trek northward after a standoff on Monday with police in riot gear, according to organizers.
Honduran President Juan Orlando Hernandez said on Tuesday some Hondurans in the caravan had already returned home. He did not specify the numbers but said the government was preparing to support them.
A Honduran migrant climbs on a truck in Quezaltepeque, Guatemala, October 16, 2018. /VCG Photo
The Honduran Foreign Ministry also called on its citizens not to join the group.
Bartolo Fuentes, a former Honduran lawmaker, and three other organizers have been detained by the Guatemalan police officers over the border.
The moves followed comments by US President Donald Trump that his administration would halt aid if the Central American governments did not act.
Fuentes has been detained because he "did not comply with Guatemalan immigration rules," according to the Honduran security ministry, adding that Fuentes will be deported back to Honduras.
Guatemala's government said it did not have official figures for how many migrants from the caravan had already crossed the border.
And security officials at the Honduran border with Guatemala in Agua Caliente blocked the road to prevent another much smaller group from getting through, television images from the border showed.
(Cover photo: Honduran riot police officers keep watch at the border checkpoint between Honduras and Guatemala, October 16, 2018. /VCG Photo)
(With input from Reuters)
Read more: Northbound migrant group doubles in size, enters Guatemala