Nigeria's main opposition candidate Muhammadu Buhari on Friday told AFP he was expecting to win next week's presidential election by a wide margin, despite talk of a close race.

The February 14 poll, in which he is challenging incumbent Goodluck Jonathan, has been seen as too close to call, leading to a possible run-off if neither man secures a first-round majority.

But Buhari, 72, dismissed the suggestion of a tight race, saying in an interview: "What's their reason for 'too close to call'? What is their speculation on? I'm expecting a landslide victory."

The former army general, who led a military government for 20 months after seizing power in December 1983, has stood unsuccessfully for the presidency three times in the last 16 years.

On each occasion (2003, 2007, 2011), he alleged electoral foul-play.

But asked if he would accept defeat this time around, the All Progressives Congress (APC) candidate stated: "I'm not going to lose. So, I won't answer that question."

Nigeria's main opposition is considered as having its best chance yet of ending the Peoples Democratic Party's (PDP) unbroken run in power since the country returned to civilian rule in 1999.

Buhari, who was noted for his hardline approach to indiscipline and corruption during his time in power, has been touted as the answer to Nigeria's lengthy list of problems.

The PDP has sought to portray Buhari as yesterday's man with dangerous, outdated ideas but he asserted that Africa's most populous nation and leading economy was ready for change.

"I have visited 34 states so far. In each of the states there are three things that are consistent, that are fundamental issues to this country -- insecurity, the destruction of the economy and corruption," he said.

"Every Nigerian is feeling worried."

-- No iron fist? --

Buhari rejected claims from the ruling party that he would rule again with an iron fist, saying the circumstances under a military regime were different from a civilian administration.

Multi-party democracy and the three tiers of government, enshrined in the constitution, had to be respected, with consequences for anyone acting outside the system, he said.

The APC has portrayed President Jonathan as weak on security and of being unable -- some say unwilling -- to end the Boko Haram insurgency in the northeast.

Some soldiers have complained that they lack the weapons and even bullets to fight the better-armed militants, despite defence spending accounting for some 20 percent of the federal budget.

Buhari said that if elected, his administration would "empower the law enforcement agencies to be much more efficient".

"The first thing we will do is to make sure there is efficient utilisation of resources. If money is voted for equipment and training, that money will go to equipment and training," he added.

The APC has claimed that Jonathan has failed to tackle endemic graft and Buhari said corruption was practically "a culture" in the country.

"I believe the most serious thing to do is to draw a line, that you intend to move forward," he said but added that investigating every allegation of corruption would be a hindrance to progress.

"From the day we are sworn in as a government, anybody who abuses trust will be called to account," he added.