(REUTERS) - The United Nations' top human rights official urged Angola's government on Wednesday to reduce the huge disparities between rich and poor that have developed in the oil-rich country despite considerable progress since the end of a 27-year civil war in 2002.

Angola, which is Africa's No. 2 oil producer, has posted rapid growth since the end of the war, but opposition parties and rights groups have long accused President Jose Eduardo dos Santos of doing too little to combat widespread poverty.

Speaking in the capital, Luanda, after a three-day visit, UN High Commissioner for Human Rights Navi Pillay praised the government for progress in rebuilding the country's infrastructure and clearing thousands of landmines.

"This development has not been without controversy," she said.

"Two issues that have consistently been brought to my attention are the huge disparities that have developed between the richest and the poorest, and the sometimes harsh methods used to evict people from land earmarked for development, especially in and around Luanda."

Dos Santos, who has been in power since 1979, was easily re-elected last year for a new five-year term during which he has pledged to improve the distribution of Angola's vast oil wealth.

His government says it cut poverty levels to about 39 per cent of the population in 2009 from 68 percent in 2002, and increased public spending in this year's budget by over a quarter to help improve social conditions.

Pillay said she stressed in a meeting with Dos Santos on Wednesday the importance of cutting the wealth disparities over the next four or five years.

The UN official said the president and Cabinet ministers accepted that problems remained and seemed genuinely committed to improving human rights.

She said, however, that the government must tackle alleged abuse - especially sexual abuse - of migrants by security forces and border officials that has persisted for the past decade, especially on the border with the Democratic Republic of Congo.

"During my visit to a remote border crossing in Lunda Norte, I received indications that sexual abuse of female migrants is continuing, as well as theft of property," Pillay said.

Recognising that the irregular entry of tens of thousands of migrants every year, many seeking to dig illegally for diamonds, causes major problems and that the government has the right to deport them, she said it must do so humanely.

Pillay said other problems included implementation of laws on freedom of expression and assembly, including the"heavy-handed" suppression of protests, and the fact that millions of Angolans, including 68 per cent of children under age 5, had not been listed in the national identification registry.