By Eric de Castro

AMPATUAN, Philippines - Philippine President Gloria Macapagal Arroyo placed two southern provinces and a city under emergency rule on Tuesday after 24 people were killed in the worst-ever election related violence in the country.

"There is an urgent need to prevent and suppress the occurrence of several other incidents of lawless violence," Cerge Remonde, the president's press secretary, told reporters.

The provinces of Maguindanao and Sultan Kudarat and Cotabato City will be under an indefinite state of emergency, which gives the military and police wide powers of arrest and detention.

The orders were issued as troops, using shovels and bare hands, dug up hastily covered graves on a grassy hillside in Maguindanao to recover the victims of the massacre on Monday.

A Reuters photographer at the scene saw 22 bodies - 14 women and 8 men - with bullet and hack wounds. Some of the dead men had their hands tied behind their back and one of the women was pregnant. Eight of those found dead were local journalists.

They were part of a group of 40 people abducted by gunmen when on their way to file a candidate's nomination to contest the governorship in elections next May. The army said it had found 24 bodies and was searching for the others.

"We are expecting that more bodies will be recovered today," Lieutenant-Colonel Romeo Brawner, military spokesman, told reporters in Manila.

The election process for the May 2010 national polls began last week with the filing of candidacies for more than 17,800 national and local positions.

Elections in the Philippines are usually marred by violence, especially in the south, where security forces are battling communist rebels, Islamic radicals and clan rivalries.

Arroyo ordered extra troops to the region and sacked the Maguindanao provincial police chief.

CLAN RIVALRY

Interior Secretary Ronaldo Puno said investigations would be completed within a couple of days and arrests made.

"There are no sacred cows," he told television. "It is going to be a direct investigation of the crimes committed. We have some information about specific names, not just those who ordered this thing, but also those who committed it."

Military officials said the dead included Genalyn Tiamzon-Mangudadatu, who was on the way to file the nomination of Esmael, her husband, to contest the governorship of Maguindanao against Datu Andal Ampatuan, the head of a powerful local family.

The town near where the massacre took place bears the name of the family.

Ampatuan has been elected governor of Maguindanao three times previously, always unopposed, although he resigned from the post earlier this year, apparently to circumvent term limits on elected officials.

One of his sons is the governor of the Autonomous Region in Muslim Mindanao, an area which covers six provinces, and the family is politically allied to Arroyo.

None of the Ampatuans made any comment to local or foreign media.

Esmael Mangudadatu, Genalyn's husband, told radio that four people had escaped the massacre and were under his care. "They will come out at the right time, they are safe with us," he said.

The southern Philippines is riven by clan rivalries, including one between the Mangudadatus and the Ampatuans. Many politicians and elected officials in the region maintain well-equipped private armies.