* President Pereira maintains June 28 election date
* Interim leader calls for investigations into killings
By Alberto Dabo
BISSAU, June 9 (Reuters) - Guinea-Bissau will hold a presidential election on June 28 as planned, the nation's interim leader said on Tuesday, a week after the killings of two senior politicians cast doubt over the poll.
A leading presidential candidate and a former defence minister were killed by military police on Friday. The authorities said they had been plotting a coup but analysts said their deaths were a continuation of political score-settling that killed the president and army chief in March.
"Having listened to all those involved in the electoral process, that is to say the political parties, civil society and the military leaders, I have decided to keep June 28 as the date for the election," President Raimundo Pereira said on Tuesday.
Pereira, who became interim leader in March after the assassination of President Joao Bernardo Vieira, made the statement on state radio after returning from talks with former colonial power Portugal.
The international community is battling to shore up the chronically unstable West African nation, which has a long history of coups and unrest.
The instability has attracted powerful Latin American drug cartels, who have exploited the lawlessness to use the impoverished, cashew-exporting nation as a transit point for shipping cocaine to Europe.
"There must be an investigation into the recent killings so the culprits are brought to justice," Pereira said, referring to the deaths of Baciro Dabo, a minister and leading candidate for the presidency, and former Defence Minister Helder Proenca.
Some parties appear ready to begin campaigning, which had been due to start on June 6 but was delayed by the killings.
However, Paulo Mendoca, an independent candidate, has already filed a complaint to the Supreme Court, saying that it would be illegal to hold polls on June 28 as the constitution calls for a delay if any of the candidates dies.
Donors and diplomats are hoping that a successful poll will pave the way for a new era in Guinea-Bissau, whose political history had been dominated by a rivalry between the late president and army chief who were killed in March.
But analysts and a former prime minister have warned that last week's killings merely underscored the need for radical military reforms to end the cycle of coups and assassinations and curb the corrupting power of drug gangs. [ID:nL6489028] (For full Reuters Africa coverage and to have your say on the top issues, visit: af.reuters.com/) (Writing by David Lewis; Editing by Nick Tattersall)