A Libyan official has raised the death toll from an attack this week at an oil field in the country's central region, saying nine guards were killed by armed gunmen.

In the Philippines, authorities said on Wednesday that three Filipino workers were among seven foreigners abducted in the same attack.

Mashallah al-Zewi, a minister in the militia-backed government in the Libyan capital, Tripoli, told The Associated Press on Thursday that the gunmen stormed the al-Mabrouk field in some 30 vehicles on Tuesday, killing the guards.

Al-Zewi says the attackers then lined up about 57 employees and lectured them about Islam before letting them go.

The field is jointly owned with Total, but the French energy company said its employees left the facility in 2013 because of increasing security risks.