Agents at a checkpoint near Tucson found nine immigrants who were being smuggled into the country locked inside the cargo area of a rental truck, officials said.

The group was found Thursday at the Interstate 19 checkpoint near Amado.

The people-smuggling attempt was called potentially deadly because of the heat and because there was no source or fresh air or way for anyone to escape the cargo area of the truck, US Customs and Border Enforcement said in a news release Wednesday.

Two people in the rental truck initially told agents that they did not have a key to the padlock of the truck's cargo door. Agents then found the keys in the cab, the release said.

The group of immigrants were processed for prosecution or for removal from the country, the agency said.