Nigeria's political opposition is demanding the resignation of President Olusegun Obasanjo -- one day after the nation's electoral commission declared him the winner of Saturday's elections, giving him a second term in office.

A coalition of 29 opposition groups Wednesday threatened unspecified action if Mr. Obasanjo refuses to step down by May 29th and allow fresh elections to take place.

The opposition called on the public to ignore the outcome of Saturday's vote and said it would go to court to mount a legal challenge.

Results tallied by Nigeria's electoral commission show Mr. Obasanjo won with 61 percent of the vote, while his main rival, Muhammudu Buhari, received 32 percent. Mr. Buhari has publicly rejected the vote -- calling it "a joke."

The former military ruler also rejected the results of parliamentary elections held 10 days ago. Official results gave Mr. Obasanjo's ruling People's Democratic Party a majority win in both houses of parliament.

After declaring President Obasanjo the winner, the chairman of the electoral commission defended the integrity of the poll. And President Obasanjo, in a televised speech, urged the opposition to accept the results and be "good sportsmen."

Several international monitoring groups have reported serious irregularities in several states during last Saturday's vote. The United States has called on Nigeria's government to address the vote-rigging allegations.

It was the first time in 20 years that a presidential election in Nigeria was held under civilian rule. Mr. Obasanjo's first election in 1999 ended 15 years of military rule.