Extra soldiers and federal police were deployed to guard Mexico's oil wells and pipelines on Wednesday after a rebel group said it caused explosions at fuel pipelines as part of an anti-government campaign.

State oil monopoly Pemex, a major United States supplier, said it beefed up its police and army presence at installations after the left-wing Popular Revolutionary Army, or EPR, said on Tuesday it was behind attacks on four pipelines in the past week. It vowed to carry out further attacks.

Pemex added two extra helicopters to its surveillance operations and was working with the defence ministry and federal police on the best way to guard the country's pipelines, which stretch over 14,000 km (8,700 miles).

"What we are doing is reinforcing this presence, particularly in our network of pipelines," a spokesman said.

Stable supplier

Mexico is the world's number nine exporter of crude oil and valued by the U.S. as a politically stable supplier.

"The army is guarding the (oil and gas) installations and, logically, we are on alert," said Andres Granier, governor of oil-rich Tabasco state where newly arrived soldiers were visible at gas processing and petrochemical plants.

Police were also deployed to guard strategic locations in Mexico City, after the federal government reacted to Tuesday's threat by saying it will ramp up national security.

"They are guarding strategic points in various places," a spokesman for the city's security ministry said.

Pipeline blasts on Tuesday and last Thursday hit domestic supplies of natural gas, liquefied petroleum gas, crude oil and gasolene in central Mexico.

Thousands of local residents were evacuated, but there were no injuries, and no impact on Mexico's crude oil exports.

Federal police are still investigating the explosions, which all occurred at around 1 a.m. local time, but the government said it was taking the threat seriously.

Despite the swift response, some commentators in Mexico say they are sceptical of the tiny rebel group's ability to conduct a serious guerrilla campaign.

Reuters