Nigerian President Muhammadu Buhari has defended David Cameron's comments, caught on video this week, about Nigeria being "fantastically corrupt."

Nigerian President Muhammadu Buhari has defended David Cameron's comments, caught on video this week, about Nigeria being "fantastically corrupt."

Buhari insisted that Cameron had nothing to apologize for, as he was merely talking about what he knows.

"I think he's being honest about it..." he told CNN's Christiane Amanpour. "I don't think you can fault him."

Speaking at an anti-corruption conference on Wednesday, Buhari said: "I am not demanding an apology from anybody, I am demanding a return of assets."

During a conversation with the Queen that was captured on camera on Tuesday, Cameron declared Nigeria and Afghanistan "possibly the two most corrupt countries in the world."

The comment came as world leaders gathered in London for an anti-corruption summit, which has been largely overshadowed by Cameron's gaffe.

The social media backlash was swift and Nigeria's presidential spokesman said they were "embarrassing to us."

A 2015 report by Transparency International, an independent anti-corruption group, scores Nigeria the world's 136th most corrupt country, out of 168. Afghanistan fares worse in the survey, coming in at number 166.

Nigeria President: Cameron 'being honest' about corruption 00:45

But President Buhari said he was more concerned with fighting corruption than talking about it. He said his administration was making inroads with clearing a backlog of "ghost workers" who are claiming salaries fraudulently and by arresting those who embezzled government funds during the previous administration.

At the opening of the anti-corruption summit today, Buhari said: "When it comes to tackling corruption, the international community has looked the other way for too long.

"Nigeria is calling on this summit to trace and facilitate the recovery of stolen funds and assets hidden in secret accounts," he added.

Afghanistan President Ashraf Ghani also called for a more concerted effort in bringing criminals to justice -- with a particular focus on drug trafficking.

"We are asking you -- and all of Europe -- to go after drug money. We need very credible action because as long as the criminal economy persists, the networks, the actions we do [will not work]," he said at today's summit.

"Billions have ended up in Europe and there has been no action for this."

Also speaking at the summit, U.S. Secretary of State John Kerry said corruption was a contributor to terrorism.

"Corruption writ large is as much of an enemy, because it destroys nation states, as the extremists we're fighting," he said.

"Corruption tears at the entire fabric of society."

Buhari had earlier told Amanpour that billions of dollars designated to fight the country's major terrorist group, Boko Haram, were shared among officials who gathered "as if they were going to have lunch and dinner and put the money into their accounts."

Oil money and blood diamonds

Nigerian President responds to reports of military abuse 02:42

Buhari said at the summit that his country had suffered from oil theft on an "industrial scale," with the proceeds being "laundered through world financial centers by transnational organized criminals."

He estimated around 150,000 barrels of oil were being stolen per day.

The Nigerian President called on the international community to designate oil theft as an international crime similar to the trade in "blood diamonds."

The theft "constitutes an imminent and credible threat to the economy and stability of oil-producing countries like Nigeria," he added.