By Saliou Samb

CONAKRY (Reuters) - At least two people were killed when Guinea security forces wielding truncheons and tear gas grenades cracked down on an opposition protest in the capital on Tuesday, hospital sources said.

Tensions are rising in the West African state ahead of a parliamentary election that the opposition says is being rigged in advance by President Alpha Conde.

A doctor at Conakry's Donka Hospital told Reuters on condition of anonymity that the hospital had received two corpses -- one apparently stabbed to death and the other apparently beaten to death.

Leading opposition figure Cellou Dalein Diallo, who had organized the rally, said three people had been killed and that security forces had used live rounds.

"We have collected bullet casings, but the clearest proof is the dead bodies," Diallo told reporters. "I'm being told now of three dead, but I am waiting for the Red Cross and the country's medical services to give me a full report."

Residents said violence had broken out in the late morning in the Conakry suburbs of Bambeto and Bomboli, strongholds of the opposition and inhabited mostly by members of Diallo's Peul ethnicity -- a group that has long complained of being denied political power despite being Guinea's largest ethnicity.

"There were youths on the hilltops throwing rocks. The security forces fired back with tear gas, which triggered general panic," Souleymane Bah, a resident of Bambeto, said.

Diallo, who narrowly lost a presidential election last November to Conde, has said the government is tampering with voter rolls to win a majority. He has also accused Conde of installing an ally as head of the electoral commission.

Guinea's military, which has been implicated in past massacres of opposition protesters, ordered its soldiers to remain off the streets on Tuesday, leaving security to the national guard and police.

Guinea Security Minister Mamadouba Toto Camara called on Guineans to "respect the authority of the state" and said police had the right to supervise the rally.

(Reporting by Saliou Samb; Writing by Richard Valdmanis; Editing by Rosalind Russell)