The president of Nigeria has challenged the Islamist militant group Boko Haram to identify themselves and state their demands as a basis for dialogue.Goodluck Jonathan said there was no doubt that Boko Haram had links with other Jihadist groups outside Nigeria.He said if they did not identify themselves, talks were impossible.It comes as the leader of Boko Haram denies killing civilians in last week's Kano bombings, in which 185 people died.In an interview with Reuters, Mr Jonathan said: "If they clearly identify themselves now and say this is the reason why we are resisting, this is the reason why we are confronting government or this is the reason why we destroyed some innocent people and their properties, why not."See, as a president of a country you will not preside over dead bodies. You will be a president of people who are alive. So if they clearly identify themselves then there will be a basis for dialogue."He acknowledged the fears of the United Nations and neighbouring governments that the groups training and arming were being bolstered by Jihadist allies such al-Qaida in the Islamic Maghreb and al-Shabaab.In Kano, Christian leaders have welcomed the President's appeal for dialogue to end the current state of insecurity.DenialThe group has acknowledged carrying out attacks on police stations and other official buildings.But in a message posted on YouTube, Abubakar Shekau blamed the deaths of "innocent civilians" on Nigeria's security forces.Nigeria's authorities deny the allegations.Last Friday's attack in Nigeria's second-biggest city was the deadliest in Boko Haram's recent campaign of violence, carried out in the mainly Muslim north.Boko Haram, whose name means "Western education is forbidden", says it wants to overthrow the government and impose Islamic law.This week security forces arrested more than 150 suspected members of the organisation.In his 40-minute audio message, Mr Shekau also threatened to carry out a bombing campaign against Nigeria's secondary schools and universities - unless security forces stopped what he claimed was a series of recent attacks on Islamic schools or madrassas in the northern town of Maiduguri.The still picture posted on YouTube shows Mr Shekau dressed in a black turban and a white gown and bullet-proof vest - holding an AK 47 rifle.He reiterated claims that the Nigerian government would not be able to stop Boko Haram - and demanded the release from prison of all its members.On Tuesday, President Goodluck Jonathan sacked the chief of police, Hafiz Ringim, forcing him to retire early, a statement from the presidency said.There had been calls for the police chief's resignation since a man suspected of masterminding Boko Haram's Christmas Day bomb attacks on churches escaped from police custody earlier this month.