Any attempt to block the entry of Central American migrants is likely to prompt legal challenges, though Trump is likely emboldened following a Supreme Court ruling earlier this summer that affirmed the president's right to bar the entry of migrants who "would be detrimental to the interests of the United States".
The federal agency says the caravan of people seeking asylum that's headed toward the Texas-Mexico border, with an unknown destination, will attract the attention of others.
This time, according to officials briefed on the discussions, Trump's aides had been looking at sending many more troops - up to 10,000 - to aid in addressing the migrant flow, as they scrambled to satisfy a president demanding a muscular response. Four days after crossing into Mexico, the caravan is still more than 3,000 kilometers (1,860 miles) from the U.S. border. In April, the Pentagon authorized 4,000 National Guard troops to head to the southern border to aid US and Customs and Border Protection. Trump tweeted on Thursday.
He vowed that he would not allow them into the country.
"If they come here illegally with no legitimate reason to stay, they absolutely will be apprehended and removed immediately", she said, adding that the migrants should seek refuge in Mexico instead.
In 2017, the USA had 331,700 asylum claims, more than any country in the world, according to the U.N. Refugee Agency.
The order would be akin to Trump's previous aggressive immigration-blocking executive orders, such as the travel ban aimed at halting people from some Muslim-majority countries from entering the U.S.
President Trump has recently increased his criticism of the caravan as it has swelled to about 7,000 people, before shrinking slightly, and warned that he was preparing to call up the military to close the border if Mexico did not stop crossings. Kirstjen Nielsen, the Homeland Security secretary, who has briefed Trump about the caravan as well as data showing a large uptick in the number of apprehensions at the border over the past year, has been leading the effort. Those troops are under the control of state governors and are limited to support roles such as providing surveillance. So far, only a little over 2,000 have been used.
The US military is prohibited from carrying out civilian law enforcement on American soil unless specifically authorized by Congress. "You're going to see a very secure border", he said.