Nigeria's President Goodluck Jonathan is urging his nation to vote peacefully and accept results of Saturday's presidential election, which analysts say will be the tightest in the nation's history.

Jonathan said in a televised broadcast Friday that no political ambition can justify shedding blood. Dozens of people already have been killed.

Jonathan and leading rival Muhammadu Buhari signed peace pledges Thursday and urged their supporters to avoid violence.

Human rights leaders says politicians have done little to lower tensions heightened by hate speech on ethnic and religious lines.

Security forces are also on high alert against attacks by Boko Haram Islamic extremists who have threatened to disrupt the vote.