UPDATE 4-Mexican oil, gas pipelines hit again by explosions

(Adds Calderon, unexploded device found, detail)

By Imelda Medina

MALTRATA, Mexico, Sept 10 (Reuters) - Explosions rocked Mexico on Monday as attacks on six pipelines disrupted oil and gas supplies and forced thousands from their homes, just weeks after leftist rebels set off a string of pipeline bombs.

Huge billowing flames lit the night sky after the blasts in the early hours of the morning. More than 20,000 people were rushed from their homes to emergency shelters as gas and oil spewed from the ruptured pipes.

President Felipe Calderon, on an official visit to India, condemned the sabotage and vowed to catch the perpetrators.

State energy monopoly Pemex said there were no injuries from the blasts, most of which were in Veracruz on the Gulf of Mexico, but Chief Executive Jesus Reyes Heroles said they would cost the company "hundreds of millions of dollars."

An undetonated explosive charge was found at another oil installation in Veracruz state, Pemex said.

In July, a shadowy leftist guerrilla group claimed responsibility for a wave of bomb attacks on energy pipelines which cut natural gas supplies to thousands of businesses.

Some local media reported on Monday that the same leftist group left a message with the unexploded device -- but local government and police officials denied any note was left. "It's just a rumor," one official said.