It is a "disgrace" for Nigeria that its neighbors have been more successful in battle against its Boko Haram insurgency than its own army, opposition presidential candidate Muhammdu Buhari said in an interview a week before the election.

Troops from neighboring Chad, Niger and Cameroon, all much smaller and poorer than Nigeria, have been battling the Islamist militants who have seized territory in northeastern Nigeria in a five-year insurgency.

Thousands of Nigerians have been killed and 1.5 million displaced in the uprising by militants known for executing and kidnapping civilians.

"It’s a big disgrace for Nigeria. It is now Cameroon and Chad fighting the insurgency more than Nigeria. We will build the capacity and Nigeria should be able to secure its territorial integrity," Buhari told Reuters.

A former military ruler, Buhari is hoping his strongman reputation will resonate with voters disheartened by incumbent President Goodluck Jonathan's failure to tackle the insurgency.

The election itself, set for Feb 14 although there has been talk of possible delays, will be another big test of security in Africa's most populous country. Eight hundred people died in violence after the last election in 2011.

In a country where the population is about 50 percent Christian and 50 percent Muslim, Buhari is a Muslim northerner and Jonathan is a Christian southerner.

Buhari said that he was committed to using the courts if there are irregularities in the voting, and would not call his followers into the streets.

"I'm optimistic that I won’t lose. But we signed an undertaking that it will be violence free," Buhari said. "We are attempting to stabilize a multi party democratic system."

The country is already on edge over reports the election may be delayed. Jonathan's ruling People's Democratic Party has put pressure on the election commission, INEC, to postpone the polls arguing it is not ready to hold them.

Buhari's opposition All Progressives' Congress insists on the date, saying the only reason the pro-Jonathan camp is pushing for a delay is that it knows he will lose if voting goes ahead now.

"There will be no delay. But if INEC is compromised then it will be too bad," said Buhari.

Buhari said his administration also intends to tackle corruption within the Nigerian National Petroleum Corp (NNPC) and plans to reopen an investigation into missing crude revenues of around $20 billion.

He would also tackle the theft of crude tapped from pipelines in the Niger River delta.

"Our main objective is to secure the country. We will not tolerate insurgency, sabotage of the economy by the blowing up of installations, by stealing crude and so on.... All these things will be things of the past."