MANILA, April 27 (Reuters) - Four people were killed and two dozen wounded when two rival politicians exchanged gunfire in a rice-growing town in the northern Philippines, police said on Friday, ahead of elections next month.

Ismael Rafanan, regional police chief, said fighting erupted late on Thursday in Jaen town when the convoy of a mayoral candidate was fired upon by suspected supporters of a congressman allied with President Gloria Macapagal Arroyo.

"We're conducting a thorough investigation because we've been hearing so many versions of what had really happened," Rafanan told reporters, adding the armed bodyguards of the two feuding politicians had been questioned.

Rafanan said fresh armed police units would be sent to ease tension in the area.

On Wednesday, Arroyo raised concern over the rising level of violence ahead of congressional and local elections on May 14 due to intense rivalry among powerful political clans and the country's trigger-happy culture.

The Philippines is also battling two insurgencies by Muslim separatists and Maoist-led rebels in 69 of 81 provinces across the archipelago of 7,000 islands.

About 8,000 soldiers have also been fighting a few hundred Islamic militants belonging to al Qaeda-linked Abu Sayyaf that beheaded seven workers on Jolo island in the south last week.

Clashes have also erupted with a rogue faction of the Moro National Liberation Front (MNLF) since April 14, threatening the holding of elections on Jolo next month.

But the elections commission said it was not planning to scrap or delay elections on the island because fighting was confined to mountains near three towns -- Panamao, Indanan and Parang.

"We were given an assurance by the military that it would stop operations 10 days before the actual elections to allow displaced families to return home and vote," Rene Sarmiento, an election commissioner, told Reuters.

"As far as we're concerned, elections would take place on Jolo on May 14." Over 140 people were killed in election-related violence in the 2004 presidential race, one of the deadliest since dictator Ferdinand Marcos was overthrown in 1986.

This year, half of the 24-seat Senate, all of the 235-member House of Representatives and nearly 18,000 of local government seats are up for grabs in the May 14 vote.

In the run-up to and during elections, private individuals are barred from carrying firearms but the ban is widely flouted with an estimated 300,000 unregistered guns in circulation.

The police have so far only collected 1,700 assorted weapons from nearly 2,000 people caught violating the ban.

The national police said powerful political barons outside Manila employ private armies and some soldiers and police officers moonlight as drivers and bodyguards, forcing officials to do surprise headcounts of personnel in the run-up to elections.

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