MANILA, Philippines?The massacre of at least 22 people in Maguindanao has exposed a brutal culture of guns, greed and money that has poisoned the Philippine political system for decades, experts said Tuesday.

The murders in the southern province Monday are feared to be only the first of many killings ahead of next year's national elections, when posts from village chiefs to the president will be up for grabs.

"This explosion of violence arises whenever there is an election," said Samira Gutoc, one of the conveners of the Young Moro Professionals, a group helping the government in peace talks with armed Muslim groups in the south.

Indeed, dozens of people are killed each election season in this impoverished and often lawless Southeast Asian nation.

Local political warlords have for generations competed for political power and the accompanying business riches that government posts offer.

These clans are well known to control private armies, who carry out assassinations and counter-attacks against rivals.

The proliferation of over 1.1 million unlicensed firearms, most of them in the hands of rebel groups or paramilitaries, contribute to the general lawlessness in many remote areas, according to police.

In one high-profile murder in the run-up to congressional elections in 2007, a member of parliament from a northern province was gunned down by an assassin hired by his rival on the steps of a Manila church while attending a wedding.

All in all, 121 people were killed in that polling season, according to national police statistics, slightly lower than the 148 who died in the 2004 national elections.

But while the problem plagues the entire country, experts say Maguindanao and other parts of the far southern island of Mindanao -- where a Muslim insurgency has waged for decades -- are particularly volatile.

"Politics in Mindanao is about ownership of power. Public office is perceived as a personal, clannish thing -- a birth right, and they would spill blood for it," Gutoc said.

She said she expected more violence in the fall-out of Monday's massacre, with relatives of those killed expected to carry out vendetta killings, called "rido" in the local dialect.

"Retaliation is a natural course of events," she said.

At least 22 people were murdered as they accompanied the wife of local official Esmael Mangudadatu to file his candidacy for governor of Maguindanao province and end the decades-old control of a rival Muslim clan.

The military said 100 heavily armed men under the control of his rival, Andal Ampatuan, seized the group of more than 40 people and later shot dead many of them.

Twenty-two bodies have so far been found, and the death toll is likely to rise, the military said.

None of the Ampatuans could be contacted, but the military maintains they suspect the family as being behind the attack.

Abhoud Syed Linga, executive director of the Institute of Bangsamoro Studies who has done research on clan fighting, said the phenomenon further complicates the Muslim insurgency that has claimed more than 150,000 lives since the 1970s.

"Some rido are sustained for generations," Linga said. "The retaliation and counter-retaliation involve the whole family or clan."

The vendetta killings, he said, are the "consequence of the absence of justice" for a perceived wrong.

"Among Muslims the value of justice is strong to the extent that it becomes a duty for family members to work for justice and reject oppression," he said.

Amnesty International said the killings underlined the danger facing civilians across the entire country in the lead-up to next year's elections.

"The government must prohibit and disband private armies and paramilitary forces immediately," said Amnesty's deputy director in Asia, Donna Guest.