Militants in the Niger Delta have been given 60 days to hand in their weapons
US Secretary of State Hillary Clinton has called on Nigeria to press ahead with democratic reform and the fight against corruption.
Speaking on a visit to Nigeria, she also praised President Umaru Yar'Adua for an amnesty to militants operating in the oil-rich Niger Delta.
Later she held closed-door talks with Mr Yar'Adua, who came to power in a widely criticised election in 2007.
Mrs Clinton is on the fifth leg of a seven-nation African tour.
The BBC's Caroline Duffield reports from the capital, Abuja, that there had been some concern at the tone that Mrs Clinton would take.
Speaking after a meeting with her Nigerian counterpart, Ojo Maduekwe, Mrs Clinton said they had discussed how the US might be able to help Nigerian reform efforts.
"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," she said.
Mr Maduekwe acknowledged mild criticism, but said: "We recognise that when we get criticisms, even from our own people, not all those criticisms are intended to annoy or provoke malevolence."
Hillary Clinton encouraged Nigeria to improve transparency
Last month, US President Barack Obama skipped Nigeria on his first official Africa trip, in what was seen as a snub for its record on governance.
But senators who had the chance to meet and talk with her to date said that this was a warm, cordial discussion.
They also said Mrs Clinton pressed them on the importance of electoral reform in Nigeria in time for elections in 2011.
US officials said Mrs Clinton would take a tougher approach in private meetings, the Associated Press news agency reported.
Mrs Clinton also said the US would follow up on Nigerian suggestions about how the US could help in tackling militancy in the Niger Delta.
Nigeria declared 60-day amnesty period in the Niger Delta in an effort to end years of militant attacks that have hobbled the oil industry.
Mr Maduekwe said the amnesty was working, and that "oil levels are gradually coming up again".
Mrs Clinton called the amnesty approach "very promising".
She also commended Nigeria's peacekeeping role in Sierra Leone and Liberia.
Mrs Clinton's visit comes in the wake of clashes between a radical Islamist sect known as Boko Haram and security forces in Bauchi and three other north-eastern Nigerian states.
She leaves Nigeria on Thursday for Liberia and will round off her trip in Cape Verde.