MANILA, May 30 (Reuters) - Armed men bombed six high-voltage power pylons in rebel-infested areas in the southern Philippines, cutting off electricity in large parts of Mindanao island, officials said on Friday.

Miguel Dominguez, governor of Saranggani province, said it would take four days for engineers to fully restore electricity service in the area, including portions of the port city of General Santos.

"This is an act of sabotage," Dominguez said after security forces found fragments of a crude bomb, detonated by a mobile phone, at one of two steel towers destroyed on Thursday in Alabel town.

Police believe Muslim rebels fighting for a separate homeland in the south were responsible for the attacks, but a power company said criminal groups may also be involved.

Four transmission towers were toppled in the Lanao provinces on Friday with improvised bombs planted at the base of the steel structures.

"Our services were disrupted this morning because of these attacks," Elizabth Ladaga, a spokeswoman for the Transmission Corp (Transco) in Lanao, said, adding Mindanao's eastern and southern portions were affected.

Ross Luga of the Davao Light and Power Company, a local distributor in Davao City, said power to vital facilities, including hospitals, was restored using generators.

Transco's Ladaga said the company had lost about 20 steel towers since the start of the year due to sabotage blamed on criminal groups attempting to extort money from them.

Military and police officials however suspect the latest attacks could be the work of Muslim rebels. (Reporting by Manny Mogato; editing by Raju Gopalakrishnan and Sanjeev Miglani)

AlertNet news is provided by