The former acting director of the federal immigration agency suggested Monday that Mexico may be unwilling to stop thousands of Central American migrants from entering its southern border.

"As far as Mexican police not being able, I would say maybe not being able - maybe some unwilling." Thomas Homan, the former head of U.S. Immigration and Customs Enforcement, said in an appearance on Fox News Monday morning.

Homan said that, unlike Mexican law enforcement, U.S. Customs and Border Protection officers based at official entry points and Border Patrol agents stationed between ports "won't step aside or step back."

"They will defend this line," Homan added.

Mexico's Foreign Ministry deployed hundreds of federal police and immigration officers to its border with Guatemala last week as a group of primarily Honduran nationals made its way there.

“Sadly, it looks like Mexico’s Police and Military are unable to stop the Caravan heading to the Southern Border of the United States, “ Trump wrote on Twitter Monday. “Criminals and unknown Middle Easterners are mixed in. I have alerted Border Patrol and Military that this is a National Emergy [sic]. Must change laws!"

Late last week, some people in the 4,000-person caravan breached the Guatemala-Mexico border.

Homan said he knew a year ago that rising monthly apprehension levels of illegal entrants would continue.

"It's very frustrating doing this job for 34 years because a lot of this could have been prevented. I've said for over a year if we didn't fix these loopholes it would happen and here it is," said Homan.

President Trump has repeatedly blamed the Democratic Party for enticing the caravan and other people who have illegally entered the country to make the journey. He said it's a result of lawmakers not fixing "loopholes" that allow the majority of families and children smuggled north not to be prosecuted and to be released form federal custody shortly after being apprehended.

“Every time you see a Caravan, or people illegally coming, or attempting to come, into our Country illegally, think of and blame the Democrats for not giving us the votes to change our pathetic Immigration Laws!” Trump tweeted Monday morning. “Remember the Midterms! So unfair to those who come in legally.”

Trump said aid to Central American countries would now be cut off or curtailed after they failed to rein in their own people.

Although Mexico and the U.S. came to an agreement last week on how to proceed with dealing with the 4,000-person caravan that originated in Honduras, the Mexican government and military was unable to stop its progression.

Last Saturday, a group of 160 Hondurans set out for the southern border of the U.S. Over the course of a week, that group grew to between 2,000 and 4,000 people, according to various estimates.

Honduras leads the world as the country with the highest murder rate. The country is home to 8.25 million people and has reported 90.4 murders for every 100,000 residents, according to the United Nations Office on Drugs and Crime.

Trump urged Mexico to stop the caravan before it gets to America's southern border. Mexico deployed hundreds of additional federal immigration officers and police to the state of Chiapas on Tuesday, and the request for the U.N.'s help was seen as a further step to take control of the situation.

Chiapas is one of two Mexican states that border Guatemala. Federal officials believe the Honduran group will try to enter Mexico from the state’s 200-mile international border.

Mexico’s Interior Ministry has warned it will only allow those granted visas to cross into the country. Those in the caravan would have had to have applied for visas at the Mexican consulates in Honduras. Mexico requires its neighbors to obtain visas in order to enter the country.