MAPUTO (AFP) - Mozambican prison authorities on Wednesday dismissed claims that guards were sexually exploiting female South African prisoners in exchange for basics, such as soap.

Director of Mozambique's prison operations, Mr Samo Goncalves, told reporters that the correctional services had "never" received reports of such abuses.

The prison authorities "believe them (the allegations) to be false and devoid of truth," he said.

Pretoria this week called for an investigation into allegations published in South Africa's Sunday Times that female inmates in the Mozambican capital were forced to have sex with prison officials in exchange for sanitary pads, soap and other basic items.

The paper cited allegations in a letter smuggled out of the country's main women's prison and said it had spoken to inmates who alleged nightly attacks.

"Sometimes, girls are forced to have sex with the warders in exchange for bread or bathing soap... we are just sex slaves," the Sunday Times quotes one prisoner as saying.

South Africa's foreign affairs ministry said in a statement that it viewed "these allegations in a serious light" and it would alert the Mozambican government.

But Mr Goncalves dismissed the claims, saying the Maputo-based jail "offers the best prison conditions".

Many of the inmates mentioned in the newspaper report are serving sentences for drug-related crimes.

Interpol said in 2010 that Mozambique was increasingly becoming a drug-trafficking hub, particularly from Brazil and Asia to Europe.

Mozambican human rights activist Augusta Eduardo said reports of sexual abuse inside Mozambican jails were "extremely rare".

"This is the first time we have heard of something like this. There needs to be an investigation to establish the truth," she said.