MANILA, June 16 (Reuters) - Suspected Islamic militants with ties to Jemaah Islamiah are believed to be behind attacks on commuter buses in the southern Philippines which killed 10 people, an army spokesman said on Saturday.

U.S. bomb experts have helped gather evidence to determine the type and make of a crude bomb that ripped through a packed bus near Davao city on the southern island of Mindanao on Friday, killing 10 people and wounding 18.

Just half an hour before, a bomb went off in another bus at a terminal in Cotabato City, also on Mindanao. There were no casualties because all the commuters had left the bus before the blast.

Major Randolph Cabangbang, spokesman for an army unit based in Davao City, said a rogue faction of the Moro Islamic Liberation Front (MILF) was believed to be responsible, based on witness descriptions of two men who left a backpack on the bus and got off.

"This group is also believed to be engaged in extortion activities," Cabangbang told reporters. "The money they collect is used in their terrorist activities, buying materials to build bombs."

The main faction of the MILF is holding peace talks with the government but renegade members are believed to be linked to the Jemaah Islamiah network and continuing their fight for an Islamic nation in the southern Philippines.

Cabangbang said U.S. bomb experts would help confirm the identity of the group making the bombs, comparing samples taken from blast sites with a database.

Security forces have tightened measures to guard bus terminals in the south, fielding plainclothes police officers on board about 200 commuter buses on Mindanao and setting up more checkpoints to restrict movements of potential bombers.

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