San Juan de Sabinas, Mexico ? Toxic gas levels inside a northern Mexican coal mine are too high for any of the 65 miners trapped inside to have survived an explosion nearly a week ago, the mining company said Saturday.

The government and scientists previously said there was little hope any of those missing would be found alive.

But a new analysis of underground air showed it was too poisonous to breathe, said Javier Garcia, a spokesman for mine owner Grupo Mexico SA de CV.

Teams of experts drilled holes into the mine Saturday to release toxic gases, and a team of foreign experts – including 10 officials from the U.S. Mine Safety and Health Administration – helped to analyze the results.

Conditions inside the Pasta de Conchos mine aren’t expected to be safe enough to recover the bodies at least until today, Garcia said.

A pre-dawn explosion Feb. 19 caused by gas built up inside the mine left the 65 miners trapped underground. Rescuers were careful not to trigger further explosions as they dug for about six days in hopes of finding survivors or the remains of those killed.