There has been a massive deployment of police officers throughout Nigeria ahead of local government elections this weekend.
President Obasanjo has been campaigning in Abuja
A leading human rights group has urged the governemnt to move to prevent politically motivated assassinations linked to the poll.
Nigerians are worried that violence may occur during the vote.
Early this month, gunmen shot dead the head of the electoral commission in the central state of Kogi.
Top police chiefs held crisis meetings throughout the country to make arrangements aimed at preventing violence and disturbances at the weekend.
President Olusegun Obasanjo had instructed the police chiefs to boost their operations following recent high profile killings and bandit attacks.
In a statement, Human Rights Watch called on Nigeria's foreign partners, who include the United Kingdom and the United States, to urge the government to act quickly and end impunity for political violence.
Correspondents say the local government elections will be a test of the popularity of the president's ruling People's Democratic Party (PDP).