AFP - Guinea's military junta on Wednesday threatened to keep opposition leaders out of a presidential election which the country's poll watchdog said would be impossible to hold anyway.

Political tensions also mounted ahead of the arrival of a UN team to investigate a massacre of opposition demonstrators in a stadium in which at least 150 people were killed, according to the UN and rights groups.

International donors have withdrawn aid in an effort to press Moussa Dadis Camara's junta into talks with the opposition.

Speaking in Burkina Faso, where President Blaise Campaore has tried to mediate in the crisis, the junta's Communications Minister Idrissa Cherif told AFP that no-one who has been prime minister in Guinea would be allowed to take part in the presidential election which is scheduled for January 31.

"The country has been pillaged, sold off, by these people, we cannot accept that," Cherif said, adding that the former leaders should face legal action.

"The new constitution that we are going to put in place will say who can be a candidate and who can't. But we cannot let these people who are not clean run the country again," Cherif said.

The move would effectively block at least three major opposition leaders who have been prime minister from running for president.

The opposition last week rejected proposals allowing the junta to stay in power while a transitional government of national unity organises new elections.

Under the proposals, junta leader Camara would be allowed to be a candidate for the presidency, something the opposition has repeatedly opposed.

Camara came to power in a coup on December 23, 2008 after the death of dictator Lansana Conte, who had led the country since 1984. Initial optimism quickly soured in the mineral-rich country however.

The opposition demonstration in a Conakry stadium on September 28 was to oppose Camara's standing for the presidency. Troops opened fire there killing between 150 and 200 people, according to rights groups. Many women were publicly raped by the soldiers.

The junta says 56 people were killed and 934 injured in the stadium.

The UN team was expected in Conakry late on Wednesday to step up an investigation into the events. An advance mission arrived in mid-November to gather testimony.

"The Guinean Organisation for the Defence of Human Rights (OGDH) has already given dozens of victim's statements, audio and video files to the (UN) technical commission," Abdoul Gadiri Diallo of the OGDH said.

He added however that several soldiers who had indicated that they were ready to testify about the killings could no longer be reached. The rights watchdog said some soldiers had been sent away on special missions while others have disappeared.

Guinea's electoral commission said the January 31 date set by the junta for the presidential election was technically impossible because of lack of funds.

"We have not even commissioned electoral materials yet, we don't have voter lists because of the suspension of financial aid by donors," commission chief Ben Sekou Sylla told AFP.

Mamadou Baadiko Bah, head of the opposition Union of Democratic Forces (UFD) said that "since the events of September 28, it is impossible to even consider free and fair elections." Bah said there was "no national consensus" for a vote.