(Corrects paragraph 20 to show Engel invited Lopez Obrador for a meeting, not a hearing.)
By Dave Graham
MEXICO CITY, April 1 (Reuters) - Mexico will help to regulate the flow of Central American migrants passing through its territory to the United States, but the root causes behind the phenomenon must be tackled, Mexican President Andres Manuel Lopez Obrador said on Monday.
Speaking after U.S. President Donald Trump on Friday threatened to close the U.S. southern border if Mexico did not halt illegal immigration immediately, Lopez Obrador said he would not have a confrontation with the United States.
"I prefer love and peace," Lopez Obrador told reporters at his regular morning news conference.
The leftist president has consistently refused to get drawn into a war of words with Trump over the border.
A senior Mexican trade official warned later that closing down the U.S.-Mexico border would cause pain on "both sides."
Most of the people caught at the frontier trying to enter the United States illegally come from three violent and impoverished countries: Honduras, Guatemala and El Salvador.
Lopez Obrador has tried to persuade Trump to address the problem by fostering economic development in Central America. But on Saturday the U.S. State Department said it was cutting off aid to those three countries.
Detentions at the U.S. border have surged in recent months, angering Trump and putting pressure on Lopez Obrador to find a solution that will prevent a shutdown of the frontier to the market for 80 percent of Mexico's exports.
Asked if it was time to put pressure on the Central American countries to do more to tackle the problem, Lopez Obrador said the causes of migration were "not being attended to" and that people needed to be offered more opportunities there.
"Obviously, we have to help because Central American migrants pass through our territory and we have to bring order to this migration, make sure it's legal," he said.
"That's what we're doing. But serenely, calmly, without a commotion and with great prudence and responsibility."
Mexico began issuing temporary humanitarian visas to some members of a migrant caravan in southern Mexico, giving priority to children and the elderly, the National Migration Institute said Monday. It said it would provide transport back to Central American countries, Cuba and Haiti, on a voluntary basis.
Earlier this year, Mexico handed out humanitarian visas liberally, but reined in the program after a surge in applications. The institute said from next month it was planning to encourage people to apply for visas in their home countries.