MEXICO CITY - Six people being tested for possible radiation exposure in a hospital in central Mexico are suspects in the theft of highly radioactive cobalt-60, a government official said Friday.

The official said the six were arrested Thursday and taken to the general hospital in Pachuca for observation and testing for radiation exposure. Once they are cleared, they will be turned over to federal authorities in connection with the case of a cargo truck stolen Monday at gunpoint that was carrying the extremely dangerous material.

The official spoke on condition of anonymity. He did not specify how the six were allegedly involved in the theft.

Hidalgo state Health Minister Pedro Luis Noble said Friday that the six suffered from skin irritations and dizziness, but that none are in grave condition and may be released soon. Only one was vomiting, a sign of radiation poisoning.

But based on the tests, "none are showing immediate signs of radiation poisoning," Noble told Foro TV.

The cobalt-60 theft triggered alerts in six Mexican states and Mexico City.