Nigerian President Goodluck Jonathan on Sunday dismissed as “blackmail” a call on him by the suspected leader of Islamist group Boko Haram to resign and convert to Islam.
Abubakar Shekau made the call in a video released online earlier this weekend, in which he also denounced US President Barack Obama.
But on Sunday, Jonathan's spokesman Reuben Abati dismissed the call.
“When Nigerians voted overwhelmingly for President Jonathan in the 2011 general election, they knew they were voting for a Christian...,” he told reporters.
“As president, Jonathan is the leader of both Muslims and Christians. It amounts to sheer blackmail for any individual or group to ask the president ... to convert to Islam,” Abati added.
“The president cannot be intimidated by any group or individual. The president will never resign. Nobody should imagine that he will succumb to blackmail”.
In the video, which was released on Saturday, Shekau told the president: “(Y)ou should abandon this ungodly power, you should repent and forsake Christianity...”.
Shekau, who was speaking in the Hausa language, also criticised Obama over Washington's decision to label him a “global terrorist”.
It was unclear when the video was made, but it marks the first time Shekau has publicly addressed the terrorist designation that the United States gave him in June.
The clip, posted on YouTube, is more than 38 minutes long. While it could not be independently verified as authentic, it was similar to previous videos of Shekau.
Addressing Obama, Shekau said: “You said I'm a global terrorist, then you are a terrorist in the next world.”
Boko Haram has carried out scores of attacks in Nigeria that have left hundreds dead as part of an increasingly deadly insurgency.
Members of the group are believed to have received training from al-Qaeda in the Islamic Maghreb in northern Mali and Western countries have been watching closely for signs of further cooperation.
Some US lawmakers have been pushing Obama's administration to label Boko Haram as a whole a terrorist organisation, but American diplomats have stressed that the group remains domestically focused.
They also say deep poverty and a lack of infrastructure in Nigeria's north must be addressed as part of the solution to the violence.
Boko Haram, which means “Western education is sin” in the Hausa language spoken in northern Nigeria, is believed to include a number of factions with differing aims. Shekau is thought to lead the main radical Islamist branch.
After a 2009 uprising that led to nearly a week of fighting, ending with a military assault which left about 800 people dead, the group went dormant for more than a year.
It re-emerged in 2010 with a series of assassinations. Bomb blasts, including suicide attacks, have since become frequent.
Its attacks have been focused in Nigeria's mainly Muslim north and a number of have occurred in the religiously and ethnically divided centre of Africa's most populous nation and largest oil producer.
The West African nation's 160 million population is roughly divided between a mostly Muslim north and a predominately Christian south.