(CNSNews.com) – “As of this afternoon, we continue to track a large group of approximately 3,500 traveling through southern Mexico with the stated intent to reach the U.S. border,” U.S. Customs and Border Protection Commissioner Kevin McAleenan told a news conference on Monday.

“We’re also aware of a second large group of migrants at the Ciudad Hidalgo border crossing between Guatemala and Mexico. Size estimates for the second group are around 3,000 and made up of family units and unaccompanied children who have placed themselves in the hand of violent human smugglers paying $7,000 per person to make the journey,” McAleenan said.

“At any given moment, there are tens of thousands of intending migrants between the Guatemala border and the U.S. border,” he added.

McAleenan said he expects the foreigners, many from Central America, to seek gaps in the border to enter this county illegally.

“For the two large groups that we are following, we have already seen the first one make unlawful entry across two international borders; and the second, still in Guatemala, has deployed violent and dangerous tactics against both Guatemalan and Mexican border security teams.

“Accordingly, we are preparing for the contingency of a large group of arriving persons intending to enter the United States in the next several weeks. Our message to the organizers and participants of this caravan is simple, as the President and Secretary Nielsen have made clear, we will not allow a large group to enter the United States in an unsafe and unlawful manner.”

McAleenan said those who attempt to cross the U.S. border illegally will be apprehended; he urged those who want to make asylum claims at ports of entry to take up the offer of protection and employment authorization already made by the Mexican government.

“The caravan has already been offered protections in Mexico. You will not be allowed to enter the U.S. the same way.” McAleenan noted that 38,000 people claiming “credible fear” to return to their home country last year were deemed inadmissible and sent back.

Asked if the beefed up border security is really necessary — or if it’s just a “political move” before the election, McAleenan said, “No, this is a law enforcement operation from CBP’s perspective, and we partner with DOD all the time to help secure our border.”

McAleenan said the CBP has to be prepared for the potential arrival of very large groups, including the one that has shown disregard for law enforcement in Guatemala and Mexico.

“And we want to be ready for that. And we think this opportunity to harden our ports of entry, to be ready for mobile deployment between ports is a better way to prepare for the potential arrival of a large group like this.”

CBP on Sunday launched “Operation Secure Line,” intended to deal with the anticipated arrival of large groups of would-be immigrants.

As part of that effort, CBP has sent special response teams to all 26 crossing points on the Southwest border, including people trained in “riot control.”

Between those 26 ports of entry, 830 Border Patrol agents are on standby, ready to deploy in the air and on the ground.

“Due to the large size of the potential caravans that may arrive at the border, however, the Department of Homeland Security has further requested the support of the Department of Defense. This is in addition to the 2,000 National Guard personnel already augmenting operations,” McAleenan said.

DOD will provide “significant air and ground transportation and logistics support” to move CBP personnel and equipment to areas where they’re needed, as well as engineering capabilities, medical support units, mobile housing for CBP personnel and planning support.

“We will not allow a large group to enter the U.S. unlawfully,” he said. “We will maintain lawful trade and travel to the greatest extent possible. We will act in accordance with the highest principles of law enforcement. We will treat intending migrants humanely and professionally at all times.

“And the safety of CBP personnel — especially our law enforcement personnel on the front lines, as well as the traveling public — will remain paramount.”