Nairobi/Abuja  - US Secretary of State Hillary Rodham Clinton on Wednesday encouraged Nigeria to tackle corruption and improve governance on the fifth leg of her Africa tour.

Nigeria is Africa's most populous nation and until last month was its largest oil producer, but it faces a raft of problems - rampant corruption, bad governance and conflict in the oil-producing Niger Delta the most prominent.

"We strongly support and encourage the government of Nigeria's efforts to increase transparency, reduce corruption (and) provide support for democratic processes in preparation for the 2011 elections," Clinton said at a news conference in Abuja with Nigerian Foreign Minister Ojo Maduekwe.

Despite the fact Nigeria is the US's fifth-largest supplier of oil, Clinton is believed to have delivered a stronger message behind the scenes to the government of what US officials call "the most important country in sub-Saharan Africa."

She met with President Umaru Yar'Adua behind closed doors later in the day to hammer the message home.

Nigeria is considered one of Africa's most corrupt states, with graft permeating every level of politics, business and society.

Analysts say the fight to peg back graft has lost momentum under Yar'Adua. Nuhu Ribadu, a prominent anti-corruption tsar who gained international respect, was forced out of office shortly after Yar'Adua came to power.

Clinton also sought an update on the status of the conflict in the oil-producing Niger Delta, where attacks by militant groups have slashed oil production by around 25 per cent since early 2006.

The attacks have allowed Angola to overtake Nigeria as Africa's top oil producer. Nigeria pumped 1.76 million barrels per day in July, compared to Angola's 1.82 million.

Militant groups say they have been fighting for a fairer share of oil profits for communities who have lost their livelihoods and suffered environmental damage.

A 60-day amnesty is in force to allow the militants to give up their arms in return for a pardon and employment, but it is not yet clear how successful the scheme will be.

Clinton called the amnesty "promising."

The secretary was also believed to have pushed Yar'Adua on electoral reforms that are supposed to avoid a repeat of 2007's farcical elections, which observers say were characterized by voter intimidation and ballot-stuffing.

Also on the agenda was inter-faith violence in the predominantly Muslim north of the country.

More than 700 people died in northern Nigeria in July when a radical Islamist sect attacked police stations.

The attack by Boko Haram - a group that wants Islamic law impemented across all Nigeria and opposes Western schools - has raised of fears of the spread of Islamic fundamentalism in West Africa.

Al-Qaeda is active in North Africa and Clinton warned that the group would be keen to expand its influence to Nigeria.

"There's no doubt in our mind that al-Qaeda and like organisations ... would seek a foothold anywhere they could find one, and whether that is the case here or whether this is a home-grown example of fundamentalist extremism, that's up to the Nigerians to determine," she said.

Previous clashes between Christians and Muslims have claimed the lives of hundreds more.

Clinton attended an inter-faith roundtable before meeting Yar'Adua and called for understanding between Muslim and Christian communities.

The secretary was also due to attend an evening forum with representatives of non-governmental organizations (NGOs) on good governance and transparency before flying on to Liberia for the next leg of her trip.

The top US diplomat is touring Africa to highlight the Obama administration's commitment to the continent, build trade links and promote better governance.

After Liberia, Clinton is expected to stop briefly in Cape Verde before returning to Washington on Friday. She has already travelled to Kenya, South Africa, Angola and the Democratic Republic of Congo.  (dpa)