U.S. authorities announced that the death toll in the tragedy of immigrants found on Monday in the trailer of a truck abandoned in the hot sun in San Antonio, Texas, has risen to 53, noting that they have arrested four people on suspicion of their involvement in smuggling these illegal immigrants.

And the US immigration authorities said that 11 survivors of this tragedy are still being treated in hospitals in the city, without specifying the severity of their situation.

A previous report released on Tuesday showed that 51 people died in this tragedy, including 39 men and 12 women. According to Mexican authorities, 27 Mexicans, 14 Hondurans and seven Guatemalans and Salvadorans were among the 53 dead, while the nationality of the remaining three dead has not yet been established.

On Monday evening, a San Antonio worker heard a distress call from a truck trailer that was parked near the road he was working on and opened the trailer door to learn of the tragedy in front of him.

The federal prosecutor in charge of the case said in a statement Wednesday night that 64 people were found in the truck’s trailer, 48 of whom died, while the remaining 16 were taken to nearby hospitals for treatment, but five of them died soon after.

Survivors are suffering from severe dehydration and exposure to high temperatures after temperatures reached about 40 degrees Celsius on Monday in San Antonio, the attorney general said.

The prosecutor confirmed that authorities had arrested four people on suspicion of involvement in the tragedy.

On Wednesday, the Mexican embassy in Washington announced that Mexico, the United States, Honduras and Guatemala would coordinate their efforts to “cooperate” in the US authorities’ investigation of the tragedy.

According to the statement, the four countries decided to form an “urgent working group” to “share information and work together to eliminate human trafficking networks.”