Nigeria's newly sworn-in president has said the troubled Niger Delta will receive his "urgent attention".
Umaru Yar'Adua admitted the elections "were not perfect"
In his inaugural speech, Umaru Yar'Adua called for an end to violence in the oil-rich but under-developed area which has led to a 25% cut in oil production.
He also admitted shortcomings in the election that brought him to power, which has been widely condemned.
The inauguration marks the first time in Nigeria's history that one civilian leader has taken over from another.
After the flamboyant ceremony, the softly spoken northern Nigerian Muslim promised he would be a new kind of leader.
"I most humbly proffer myself as a servant leader. I'll be a good listener... and serve this nation with honesty, transparency, accountability, absolute fear of God and with absolute humility," he said at the inauguration in the capital, Abuja.
He also pledged to tackle corruption, which he admitted was "central" to the poverty of most Nigerians.
"We are determined to intensify the war against corruption - this is an area where we have made significant progress in recent years and will maintain the momentum."
Small demonstrations were held in the largest city, Lagos, where protesters said they were mourning the death of democracy in Nigeria.
Five of them were arrested as they carried a mock coffin of outgoing President Olusegun Obasanjo.
Nigeria is Africa's largest oil producer but attacks and kidnappings of foreign oil workers by Niger Delta militants have hit production and contributed to a spike in global oil prices.
"I urge all aggrieved communities groups and individuals to immediately suspend all violent activities and respect the law," Mr Yar'Adua said.
"Let us allow the dialogue to take place in a conducive atmosphere," he appealed to the militants who have been demanding a larger share of oil wealth for local communities.
Although Nigeria's oil money comes from the Niger Delta, the majority of the region's people remain deeply impoverished.
The BBC's Alex Last in Abuja says the problem is that the vast wealth generated from the country's natural resources has fed the few in the political elite and their personal interests.
Corruption has become so ingrained, it will be difficult to defeat, he says.
But with a new leader comes a degree of hope that maybe he will really be able to make a difference, he adds.
"I think the first task before the new president is to heal the wounds - there have been deep divisions in the Nigerian politics arising from these elections," one voter told the BBC after the inauguration.
Mr Yar'Adua, who won a landslide victory in April, did admit the elections "were not perfect".
Militants are demanding more oil wealth for the Niger Delta
"However, we have well-established legal avenues of redress and I urge anyone aggrieved to pursue them. I also believe that our experiences represent an opportunity to learn from our mistakes," he said.
He pledged to improve the way elections were conducted.
"I will set up a panel to examine the entire electoral process with a view to effecting reforms and ensuring that we raise the quality and standards of our general elections to meet international standards.
"I will make this a national priority at the conclusion of the legal processes."
The election commission, Inec, has denied charges that it favoured the ruling People's Democratic Party during last month's elections.
The two main opposition candidates have challenged the results in court.
Our correspondent says President Yar'Adua will have to prove his independence from Mr Obasanjo, who picked his successor and remains chairman of the ruling PDP.