Border Patrol officers encountered more than 144,000 undocumented immigrants at the southwest border in May, the largest monthly total in 13 years, officials said Wednesday.

More than 132,000 were stopped while crossing the border illegally; the rest presented themselves at legal ports of entry, Customs and Border Protection officials said.

May marked the third month in a row that more than 100,000 immigrants were taken into custody at the border amid a surge of migrants heading north in large groups from the Northern Triangle countries of Guatemala, Honduras and El Salvador.

More than 19,000 immigrants are currently in CBP custody. Nearly 1,000 border patrol officers have been moved from northern ports of entry, airports, sea ports and elsewhere along the southwest border to assist border agents in areas experiencing the highest influx of migrants.

"We are in a full-blown emergency, and I cannot say this stronger: The system is broken," said acting CBP Commissioner John Sanders.

Of the 132,000 who were caught entering the country illegally, more than 84,000 were traveling as a family unit, 36,000 were single adults and 11,000 were unaccompanied children.

So far this fiscal year, 610,000 immigrants have been apprehended by CBP for illegally crossing between ports of entry. If the current numbers continue, they could surpass 2006 levels, said one official.

The monthly figures were released on the same day that American and Mexican officials are slated to hold high-level talks at the White House to discuss President Donald Trump's threat to impose tariffs on Mexican goods.

Trump has vowed to punish Mexico with potentially crippling tariffs unless it does more to to halt Central American migrants from reaching the U.S. southern border.

The president has threatened to apply tariffs of 5 percent on all Mexican goods next week and increase the rate to 25 percent in coming months if Mexico fails to stanch the flow of migrants heading to the U.S.

Several Republican senators raised objections to Trump's plan on Tuesday.

But on Wednesday, the president signaled that he wasn't willing to back down.

"Mexico, you know, wants to make a deal," Trump said during a trip to Ireland. "They have their entire delegation right now going over to probably the White House location to negotiate with our people."

"The drugs that are coming in, the people that are coming in unchecked, they’re swamping our border," Trump added. "They're coming up by the millions. Mexico can stop it. They have to stop it. Otherwise, we just won’t be able to do business. It’s a very simple thing."