WASHINGTON (CN) – With border arrests up nearly three times what they were last year, President Donald Trump tweeted Monday night that he plans to have millions deported next week.

“They will be removed as fast as they come in,” Trump wrote, going on to praise Mexico for its work of “stopping people long before they get to our Southern Border.”

The tweet came over a week after U.S. Customs and Border Protection tallied 132,887 border arrests for May, up 32 percent from 51,862 in 2018.

Offering an explanation of Trump’s message, an administration official who spoke on the condition of anonymity said the removal effort would focus on the more than 1 million people who remain in the country despite having been issued final deportation orders.

The tweet from the president also described Guatemala as “ready to sign a Safe-Third Agreement,” a treaty that would effectively bar almost any asylum seeker who sets foot in Guatemala from later lodging a claim in the United States because Guatemala is deemed “safe.”

Since 2004, the U.S. has had only one Safe Third Country Agreement, with Canada.

Mexican officials have publicly rejected Trump’s push for another such deal, and no other reports have been made about any agreement with Guatemala.

This month’s CBP report breaks down the border arrests by demographic: families, single adults and unaccompanied minors.

Up from 8,900 in April and 8,968 in March, 11,507 unaccompanied alien minors were detained at the border in May.

For context, Health and Human Services reported in 2018 that U.S. border shelters were 92% full at 15,000.

Immigration and Customs Enforcement specified in the June 7 report that 72 unaccompanied alien minors were deemed inadmissible in May.

President Trump’s tweet on Monday blamed Democrats in Congress with the contributing to the border crisis.

“They must vote to get rid of the loopholes, and fix asylum! If so, Border Crisis will end quickly!” he tweeted.

Mexican officials reported Monday that the country has sent 791 new immigration agents to the U.S. border and promised about 6,000 National Guard by Tuesday.