By Justin Pearce BBC correspondent in Luanda

An internal report by the International Monetary Fund (IMF) has found that nearly $1bn disappeared from Angolan Government finances last year.

The sum is far greater than the value of humanitarian assistance sent to the country this year and the report adds that over the past five years a total of over $4bn are unaccounted for.

Frequent dialogue with the authorities and significant technical assistance in recent years has yielded little progress in the key areas of governance and fiscal transparency.

IMF report

The Angolan Government has denied the accusations

Angola has often been accused of corruption in the past, but this is the first time that financial mismanagement on such a scale has been reported by an institution with the status of the IMF.

The International Monetary Fund's stark assessment of the Angolan government's finances are revealed in a report circulated earlier this year within the IMF, and obtained recently by the BBC.

Cautious estimate

The report says that last year alone, more than $900m went missing.

The document notes that there has been little progress in the areas of governance and fiscal transparency in Angola, despite encouragement and assistance from the IMF.

The report does not mention where the missing money has gone to, but its overview of the political and economic situation in the country speaks of "extensive corruption" as one of the challenges faced by the government.

It adds that a lack of useful data made the monitoring of Angola's fiscal situation difficult.

As the country recovers from decades of civil war the money is much needed

A source suggested that the figures mentioned in the report might err on the side of caution.

A spokesman for the Angolan Finance Ministry, Bestos de Almeida, said the government had studied the report, but denied the discrepancy of billions of dollars in public accounts.

He said that the government was taking steps to improve transparency in the way it manages its money, and also to fight corruption.

The report singles out the state oil company Sonangol, with which multinational oil firms are obliged to work in partnership.

"Reported revenues from Sonangol cannot be easily be reconciled with its share of oil receipts... Further complicating the monitoring of oil revenues from Sonangol, the company assumed some time ago complete control of foreign currency receipts from the oil sector, and stopped channelling them through the central bank as mandated by the law."

A Sonangol spokesman could not be reached for comment.

The IMF representative in Angola, Carlos Leite, said he could not comment on the report, since it is an internal document and the government has blocked its publication.

The Angolan Government has in the past been accused of wide-scale corruption.

Individuals profiting

Diplomats say that at least some of the discrepancy identified by the IMF may be due to bad accounting practices on the side of the government.

But they also say that it is likely that certain individuals may have taken of advantage of the smokescreen provided by slack financial management in order to divert funds into their own bank accounts.

The sum of $900m reported missing last year is about three times the value of the humanitarian aid received by Angola this year.

Foreign donors have expressed concern that Angola's own finances are not being put to better use.

As Angola recovers from decades of civil war, the need for aid is recognised, but donor countries say they will continue to push for better financial management by the Angolan government.