* Presidential contender Karua had intended to use venue
* Kenya sent troops to fight rebels in Somalia
* Garissa has borne brunt of attacks blamed on Shabaab (Adds Karua quotes)
By Abdisalan Ahmed
GARISSA, Kenya, Feb 17 (Reuters) - A man was killed when the bomb he was apparently trying to assemble near a Kenyan primary school before it hosted a presidential candidate's rally exploded, police said on Sunday.
Residents heard a blast late on Saturday night in the eastern frontier town of Garissa but police said they only identified the site of the explosion caused by an improvised explosive device (IED) at a primary school field on Sunday.
Martha Karua, the only female presidential candidate in the March 4 vote and among the lower-ranked contenders according to most polls, had been expected to speak at the grounds on Sunday afternoon, regional police chief Charlton Mureithi said.
"Our initial assessment reveals the man was trying to set up an IED near the dais, but killed himself as the device exploded on him, ripping his body into pieces," Mureithi told reporters.
The open field also lies next to an army camp in a town used as a support base for Kenya's military mission in Somalia.
There was no immediate claim of responsibility for the intended attack, police said.
Karua kept her date with her supporters in the town but spoke from a different venue.
"I would have loved to hold this gathering in the open place where terrorists planted explosives last night," she told a crowd, pledging to improve security if elected.
Kenya has experienced a spate of violent attacks, mostly in the capital and close to the Somali border, since it sent soldiers into its anarchic neighbour in October 2011 to drive out al Shabaab Islamist rebels linked to al Qaeda.
The rebels have promised to retaliate and have launched grenade and gun attacks that have raised concerns over how secure the country is heading into the March 4 national elections, the first since tribal fighting killed about 1,200 people following a disputed presidential vote in 2007.
Garissa, a market centre for trade in camels, donkeys, goats and cattle some 200 km (120 miles) from the Somali border, has borne the brunt of the attacks. The largely Muslim town has a significant ethnic Somali population.
In October, Kenyan soldiers and Somali forces seized Kismayu, al Shabaab's last big urban stronghold in southern Somalia, driving the militants out.
"Its by the grace of God that the person who was planning evil died. Many people would have lost their lives if that mission succeeded," said Abdi Jama'a, a local resident. (Writing by James Macharia; Editing by Jason Webb)