Army soldiers stand on a road as a fire rages near the town of Omealca, in the Gulf state of Veracruz, Mexico. Six explosions believed to be the result of sabotage ripped natural gas pipelines for Mexico's state oil monopoly early Monday, sparking fires and prompting authorities to evacuate thousands of people and shut down two highways.

Veracruz, Mexico ? A shadowy leftist guerrilla group took credit for a string of explosions that ripped apart at least six Mexican oil and gas pipelines Monday, rattling financial markets and causing hundreds of millions of dollars in lost production.

The six explosions could be seen miles away, and set off fires that sent flames and black smoke shooting high above the Gulf coast state of Veracruz.

At least a dozen pipelines, most carrying natural gas, were affected, said Jesus Reyes Heroles, the head of Mexico’s oil monopoly Petroleos Mexicanos, without providing specifics.

He said there would be hundreds of millions of dollars in lost production and about nine states and the capital, Mexico City, would be affected.

“It is a big blow,” he said. “You can’t store natural gas or transport it by truck.”

The blasts caused brief jitters in international markets, with natural gas futures up as much as 20.2 cents on news of the explosions, although prices dropped in later trading. One oil pipeline was hit in Monday’s attack but Pemex said the damage wouldn’t affect crude exports.

Some local factories were forced to shut after natural gas supplies were cut. Residential supplies were not expected to be affected.

There were no immediate reports of injuries directly caused by the explosions and fires, although Fernando Leon Yepez, a civil defense official in Omealca, reported that two elderly women died of heart attacks shortly after the explosions.

It was the second time in three months that the so-called People’s Revolutionary Army claimed responsibility for a pipeline attack as part of what it has labeled its “prolonged people’s war” against “the anti-people government.”

The group, known as the EPR, is a secretive, tiny rebel group that staged several armed attacks on government and police installations in southern Mexico in the 1990s. It was later weakened by internal divisions, leaving it unclear which splinter group may have carried out Monday’s attacks.

The EPR claimed responsibility for a July attack on a major gas pipeline from Mexico City to Guadalajara in western Mexico that forced at least a dozen major companies, including Honda Motor Co., Kellogg Co. and The Hershey Co., to suspend or scale back operations.

That attack sent the Mexican government scrambling to increase security at “strategic installations” across Mexico. It was not clear what security measures were in place at the pipelines that exploded Monday.

Separate tanker crash

In northern Mexico, in an unrelated event, a truck carrying ammonium nitrate to a mine caught fire after a highway crash and blew up, killing at least 34 people and injuring some 150, state and federal officials reported Monday.

Authorities said two trucks smashed into each other Sunday night on a busy highway in northern Mexico near Piedras Negras, drawing a crowd of curious onlookers as well as a small army of police, soldiers, emergency officials and journalists.

Shortly after the crowd gathered, the wreckage caught fire, and the ammonium nitrate exploded, sending a ball of fire into the sky that consumed nearby cars and left a 10-by 40-foot crater in the road.

Officials said they did not know what caused the initial crash.

“Everyone who was a witness to the accident is dead,” said a federal police official, Alejandro Gonzalez.