* Some attackers "had Liberian accents"
* Rights groups suspect foreign mercenaries
* State TV says Medvedev sends independence day letter
(Adds Medvedev letter, naming of mediator)
By Saliou Samb
CONAKRY, Oct 2 (Reuters) - Foreign gunmen, including some speaking English with Liberian accents, took part in the mass killings of anti-government protesters in Guinea this week, witnesses and other sources said on Friday.
Their statements contradicted those of junta chief Captain Moussa Dadis Camara who blamed uncontrollable elements within the Guinean army for the killings of scores of demonstrators at a rally in the capital Conakry on Monday.
The presence of foreign mercenaries, if proven, could lend weight to accusations by Guinean rights groups that the killings of at least 157 people were organised rather than the actions of unruly army units.
"Among those who shot on people were some odd individuals who were not wearing the regular army uniform properly. They were speaking a language I do not understand," said Mouctar Diallo, an opposition leader who was beaten during the rally.
A Guinean U.N. official who did not want to be named said he was beaten up by armed men speaking English with an accent from neighbouring Liberia.
"They were drunk and clearly on drugs," he added.
Guinea and Liberia have a history of tensions, with Liberia accusing its northern neighbour of backing rebels responsible for triggering its 1999-2003 civil war.
Camara took control of the world's top exporter of the aluminium ore bauxite in a bloodless coup last December and has so far not fulfilled a promise to ensure a speedy transition to civilian rule.
Investors were unnerved last month after Guinean authorities said they would rescind the 2006 sale of the Friguia alumina refinery to Russian metals giant UC Rusal.
International condemnation of Monday's crackdown has been widespread, and ex-colonial power France has suspended longstanding military cooperation with Guinea.
State television said Russian President Dmitry Medvedev had sent Camara a congratulatory letter on the 51st anniversary of Guinea's independence on Friday. No other foreign head of state was reported to have done so.
"HUMAN TIDAL WAVE"
In brief comments to Reuters late on Thursday, Camara repeated accusations that the opposition shared blame for the violence by calling on some 50,000 supporters to turn up for the rally in a stadium in Conakry.
"They knew that with this tidal wave of humanity that they did not have the power to control their supporters. They knew what was going to happen," he said in the interview.
"Their aim was to say that President Dadis should not be candidate (in a Jan. 31 election). I think it was premeditated."
Conakry has been quiet since Monday's killings but witnesses said security forces used teargas to disperse thousands of relatives of victims who had come to collect bodies delivered outside a mosque by the army on Friday.
Authorities say the death toll stands at 57 and that many of those dead were victims of a stampede.
Separately, the ECOWAS grouping of West African states said in a statement it had named Burkina Faso president and long-time regional crisis mediator Blaise Compaore to push for talks between the junta and Guinean opposition forces to ensure January's election was credible. (Additional reporting by Emmanuel Braun in Conakry and Mathieu Bonkoungou in Ougadougou; editing by Robin Pomeroy) (For more Reuters Africa coverage and to have your say on the top issues, visit: