MANILA (Reuters) - Gunmen kidnapped and killed at least 21 people in the southern Philippines on Monday, apparently in a bid to prevent one of them filing her husband's nomination for elections next year, the military said.

Lieutenant Colonel Romeo Brawner said the bodies of 13 women and eight men were found in the area where about 30 people were taken hostage.

"We believe more bodies are buried in the ground," Brawner said. "Unfortunately the killing happened before our troops got there."

A woman planning to file her husband's nomination for provincial governor in elections next May was among those killed, other military officials said. The others with her included two lawyers and several journalists, the military said.

(Reporting by Manny Mogato; Editing by Raju Gopalakrishnan)