DAURA, Nigeria, April 21 (Reuters) - Troops shot dead three boys during a protest against alleged rigging in Nigeria's presidential election on Saturday, hospital sources said.

The sources in Daura, northern Nigeria, said 10 other people were wounded when soldiers opened fire during a protest in the town by opposition supporters.

"There were seven people shot by the military, three of whom are dead," a source at Daura general hospital told Reuters. The boys were aged between 11 and 17, the source said.

No other details were immediately available.

Daura is the hometown of former military ruler Muhammadu Buhari, the main opposition candidate in Saturday's election.

Buhari told Reuters more street protests were likely from Monday onwards if the ruling People's Democratic Party (PDP) claimed victory after the election. Observers and witnesses reported widespread rigging and a massive shortfall of ballots during the vote in Africa's most populous nation.

"It is likely we will call our supporters as from Monday to come out and protest if the PDP announce they have won the election," Buhari told Reuters in an interview.

"It is not a question of winning because I don't think there have been elections."

In Kano, a Buhari stronghold, electoral officials said only half the required ballots arrived in time for the election.

The electoral commission in Abuja said all 65 million ballots were distributed nationwide and it was unclear what had happened to voting materials reported missing around the country.

President Olusegun Obasanjo, who is standing down in the election after serving two terms, denied there had been vote rigging. "This government has no reason to tamper with election results," Obasanjo said.

AlertNet news is provided by