* Military police kill presidential candidate
* Authorities say operation meant to foil coup attempt
* Former prime minister and defence minister also dead
(Updates with intelligence services statement)
By Alberto Dabo
BISSAU, June 5 (Reuters) - Military police in Guinea-Bissau on Friday killed a government minister who was to be a candidate in presidential elections in what they said was an operation to foil a planned coup attempt.
Territorial Administration Minister Baciro Dabo and former defence minister Helder Proenca were shot dead in what the intelligence services described as a bid to prevent a coup in the notoriously unstable former Portuguese colony.
Local radio said former prime minister Faustino Embali, who was seized by the security forces in the operation, was also later killed.
"This was about nipping a coup attempt in the bud. Among the authors of this coup some came quietly while others tried to resist, that is why they were killed," the state intelligence services said in a communique.
"We have material proof that this coup attempt was aimed at physically eliminating the head of the armed forces, overthrowing the interim head of state and dissolving the national assembly," the statement said.
In March, soldiers killed President Joao Bernardo "Nino" Vieira in an apparent revenge attack for the slaying of the army chief of the West African country.
Guinea-Bissau has become a transit point for drug smuggling, where coups and political violence have been commonplace since independence in 1973.
The U.S. State Department said in its annual narcotics survey in February 2009 that Guinea Bissau risked degenerating into a narco-state.
Campaigning for elections, which are scheduled for June 28, is due to begin on Saturday.
Dabo, a close ally of Vieira, was seen as a serious candidate with a strong chance of winning the poll. Proenca was a defence minister in Vieira’s administration.
"Men in uniform came in a four-wheel-drive vehicle and entered (Dabo’s) house," a witness said.
The deaths of Vieira and army chief General Batista Tagme Na Wai ended a long, violent feud between the two, but analysts say a power vacuum in the deeply impoverished country could allow Latin American cocaine cartels, already active in Bissau, to extend their influence.
Drug smugglers are increasingly using poorly policed West African states as staging posts for shipments from Latin America to lucrative markets in Europe. (Writing by Daniel Magnowski; Editing by Giles Elgood)