U.S. Border Patrol agents found the bodies of four people, including three children, near the Rio Grande River in southern Texas on Sunday.
Hidalgo Country Sheriff Eddie Guerra tweeted that the bodies appear to be that of a 20-year-old woman, two infants and a toddler. He told the McAllen Monitor that they may have been dead for a few days.
The discovery was made southeast of Anzalduas Park in Las Paloma Wildlife Management Area, an area often used for illegal border crossing.
U.S. Customs and Border Protection says the area “accounts for more than 40 per cent of illegal alien apprehensions.”
Guerra said because the bodies were found on federal land, the FBI will lead the case.
While the investigation is ongoing, officials told KRGV they are looking into dehydration as a possible cause of death. Foul play is not suspected.
In the month of May alone, Border Patrol officers encountered more than 144,000 undocumented immigrants at the southwest border, NBC reported this month. The number is said to be the biggest monthly total in 13 years.
WATCH: Trump says immigration raids are ‘going by the law’
A roundup of undocumented families was expected to start across the U.S. on Sunday, but the plan was delayed by President Donald Trump one day earlier.
In a tweet, Trump said he deferred the raids for two weeks to “see if the Democrats and Republicans can get together and work out a solution to the asylum and loophole problems at the southern border.”
“If not, deportations start,” he said.