"Apparently it is sabotage," said Wilfredo Silva, head of the armed forces unified command.
Energy Minister Rafael Ramirez told state television that the fires were under control, and dismissed suggestions that it would result in a fuel shortage.
Assistance
The pipeline moves crude oil to a massive refining complex on Lake Maracaibo, Ramirez said.
Chavez, who heads Latin America's only OPEC member, has courted nations across the Caribbean with cut-rate oil and offered cash-strapped Argentina financial assistance.
He led a coup attempt in 1992, was elected president in 1998, reelected in 2000, survived a coup in 2002 and fought a recall referendum last year.
Huge spending on welfare and health, paid for with Venezuela's oil wealth, have sustained his strong support among many Venezuelans.
RSS