Illegal crossings on the border with Mexico climbed in April to triple the year-earlier levels, the US Department of Homeland Security said on Friday, warning undocumented immigrants they will be prosecuted.
With the Trump administration concerned that its crackdown on illegal immigration is not working, DHS said 50,924 people were apprehended in April trying to enter the United States illegally from Mexico.
That was the highest level for April since 2014, an increase of more than 600 people over March, and up from 15,766 people detained a year ago, in a sharp immigration downturn that followed the election of President Donald Trump.
The numbers of unaccompanied children, 4,314, and family units, 9,647, also rose compared with March.
DHS says the level of detentions is a strong indicator of the overall flow of illegal immigration, and a surge in detentions is a sign of a concomitant jump in successful entries by paperless migrants.
The latest numbers "underscore the continuing security crisis along our southwest border," said DHS spokesman Tyler Houlton.
The increase came as a well-publicized caravan of families and children from violence-plagued central America marched through Mexico during April toward the US border, many saying they would seek asylum.
Media coverage of the US-bound caravan triggered a flurry of furious tweets from Trump, who ordered thousands of National Guard troops to the border and called on Mexico to stop the migrants.
The caravan set out with 1,000 people, but most later dispersed, leaving some to travel on their own.
Mexican officials said on Thursday that 145 had so far entered the United States to seek asylum -- a process that can separate parents from their children -- while about 150 others remain at a camp in the border city of Tijuana, Mexico.
The US Justice Department said it had arrested and charged 11 members of the caravan for illegally entering the United States.
US authorities are seeking tougher legal powers to prevent and deter illegal immigration.
"To those seeking to abuse our generous laws -– we are watching. We will not sit back and watch our laws exploited," Houlton warned in a statement.
"If you make a false immigration claim, you will be referred for prosecution. If you assist or coach individuals in making false immigration claims, you will be referred for prosecution."
Trump wants to build a border wall against illegal migrants, and has repeatedly tried to link immigration with crime.