ARMED SOLDIERS

Trump said on Twitter on Monday that the military would be waiting for the procession -- suggesting a far more direct role in confronting the migrants than the Pentagon described.

"Many Gang Members and some very bad people are mixed into the Caravan heading to our Southern Border," Trump tweeted.

"Please go back, you will not be admitted into the United States unless you go through the legal process. This is an invasion of our Country and our Military is waiting for you!" he added.

Trump administration officials have been discussing other options to address the caravan and a surge in border crossings, including having Trump use his authority under the Immigration and Nationality Act to declare certain migrants ineligible for asylum for national security reasons.

Officials said no decisions had been made.

Kevin McAleenan, the US commissioner of Customs and Border Protection, said a group of approximately 3,500 immigrants were traveling through southern Mexico with the intent of reaching the US border.

A second caravan of about 3,000 people were at the Guatemala-Mexico border, McAleenan said.

At the same time, over the last three weeks, border agents have encountered nearly 1,900 people per day either crossing the border illegally or presenting themselves at ports of entry, with over half of them being children alone or parents and children traveling together, McAleenan said.

"We are already facing a border security and humanitarian crisis at our southwest border," he said.

Some migrants have abandoned the journey, deterred by the hardships or the possibility instead of making a new life in Mexico. Others joined it in southern Mexico.

Trump's decision to call in the military appears to be a departure from past practice, at least in recent years, in which such operations were carried out by National Guard forces -- largely part-time military members who are often called upon to serve in response to domestic emergencies.

There are already 2,100 US National Guard forces at the border, sent after a previous Trump request in April. The latest deployment would be in addition to those forces.

The decision to send active duty forces this time gives the Pentagon the ability to more rapidly mobilize greater capability than would be immediately available with the Guard, officials said.

But it also injects the military, which prides itself in being non-partisan, into a highly charged political issue just days ahead of an election.

Reuters