A woman fries beans cake along a street after days of religious clashes in the northern Nigerian city of Maiduguri, August 4, 2009. [Agencies]

Big oil revenues are a curse instead of a blessing to ordinary Nigerians and Angolans. Analysts note that petrodollars allow their leaders to ignore foreign critics, unlike other states on Clinton's itinerary that rely on foreign tourism, aid or peacekeepers.

The two nations are nominally democratic, but politicians feel little need to court voters.

Nigeria has a history of coups and the last elections here were marred by voting irregularities and police firing tear gas at lines of voters. In Angola's last parliamentary election, money, alcohol and even cars were dished out and many polling stations didn't open for lack of materials, international observers found. Angola was in civil war from the 1970s to 2002. It has not held presidential elections since the war ended.

"Despite the widespread perception that government corruption at all levels was endemic, there were no public investigations or prosecutions of government officials during the year," said a report this year by the US State Department.

More than two-thirds of 12 million Angolans and more than four-fifths of 150 million Nigerians live on less than $2 a day. Many feel neglected by their leaders.

"They don't care about the small man. Not at all," said Sam Olufemi, selling phone cards amid one of Lagos' perennial traffic jams. "It's pay-as-you-go politics."

Angola has suffered unrest in Cabinda, the main oil-producing region. Human rights groups have accused the military of atrocities and claim government officials have embezzled millions of dollars in oil revenue. The government has denied the charges.

Thousands have been killed over the years in Nigeria's oil-rich Delta, where the military battles criminal gangs by firing into slums from helicopter gunships and militant groups bomb pipelines and kidnap foreigners.

Diarmid O'Sullivan of Global Witness said one way the US Congress could help is by passing the Extractive Industries Transparency Disclosure Act, which would require oil, gas, and mining companies listed on US exchanges to publicly disclose their payments to the governments of countries whose riches they extract.

The bill was introduced in Congress last year but didn't pass. Campaigners are hoping it will be reintroduced this year.

AP-Xinhua