EDINBURG, Texas — Police in Texas acting on a tip found 17 immigrants locked inside a tractor-trailer parked at a gas station about 20 miles from the border with Mexico, less than a month after 10 people died in the back of a hot truck in San Antonio.

Edinburg Assistant Police Chief Oscar Trevino told ­KGBT-TV that the immigrants from Mexico, Honduras, Guatemala, and Romania may have been locked inside the 18-wheeler for at least eight hours before being freed by officers Sunday morning.

None of the people inside the tractor-trailer required medical attention. A man and woman who Trevino said are Cuban nationals were in charge of the rig and have been detained.

The discovery came three weeks after 10 people died in a sweltering rig parked at a Walmart in San Antonio. Of the 39 immigrants inside the when rescuers arrived, 10 were dead and 20 were hospitalized in dire condition. The driver was charged with illegally transporting immigrants for financial gain, resulting in death.

On Sunday, Edinburg police went to the gas station after receiving an anonymous call from someone saying a relative was trapped inside the tractor-trailer. Officers began knocking on the sides of all the trailers parked at the station and eventually received return knocks from the one holding the immigrants, police said.

The two cases demonstrate how smugglers regularly use big rigs in an elaborate network of foot guides, safe house operators, and drivers.

ASSOCIATED PRESS