Fifty-five people who were government ministers, state governors, public officials, bankers and businessmen stole 1.34 trillion naira ($6.8 billion) from Nigeria's public purse over a seven-year period, the information minister said on Monday.

Endemic corruption has enriched a small elite but left many Nigerians mired in poverty despite the country being Africa's top oil producer and having the continent's biggest economy.

President Muhammadu Buhari, a 73-year-old former military ruler, took office in May after winning an election largely fought on his vow to crackdown on corruption.

Since then corruption charges have been levelled against a former national security adviser and a former defence minister, and the president last week ordered the investigation of ex-military chiefs for an alleged arms procurement fraud.

Speaking in the capital, Abuja, to launch a corruption awareness campaign, Information Minister Lai Mohammed told reporters around $6.8 billion was stolen between 2006 and 2013.

"This is the money that a few people, just 55 in number, allegedly stole," said Mohammed, adding "the time to act is now" to address what he called "Nigeria's war".

He gave a breakdown which included the theft of 147 billion naira ($742.42 million) by 15 former state governors, 524 billion Naira ($2.65 billion) by bankers and 7 billion naira($35.35 million) he said was stolen by four former ministers.

"If we don't kill corruption, corruption will kill Nigeria," added Mohammed, who did not provide any proof to support the figures he provided.

Buhari has said his government will recover "mind-boggling" sums of money stolen from the oil sector and that public coffers were "virtually empty" when he took over from his predecessor Goodluck Jonathan.

Buhari's presidency ended a period from 1999-2015 when the People's Democratic Party (PDP) was in power. The PDP, now in opposition, has accused the president of mounting a witch-hunt against its members.