Kumba Yala, the third-placed candidate in Guinea-Bissau's presidential election, has thrown his support behind former military ruler Joao Bernardo "Nino" Vieira in the second round run-off which will take place on 24 July.
His decision to support Vieira will make it more difficult for Malam Bacai Sanha, the frontrunner in the first round of the election, with 35 percent of the vote, to maintain his lead.
Yala, who won 25 percent of the vote in the first round on 19 June, announced his support for Vieira, who achieved 29 percent, in a statement on Saturday.
"Joao Bernardo Vieira is a symbol of the construction of the Guinean state and of national unity because he proclaimed our independence in the hills of Boe," Yala said, referring to Vieira's role as a guerrilla commander in the fight against Portuguese colonial rule in the 1960s and early 1970s.
"Of the two candidates, he is the one who for me can be relied upon to defend our national independence, to oppose neo-colonialism, to build the republic and promote peace, stability and above all, national reconciliation," Yala said.
First round front-runner Bacai Sanha is the official candidate of the ruling African Party for the Independence of Guinea Bissau and Cape Verde (PAIGC).
However, Yala's decision to support Vieira was unpopular with many people within his own Social Renovation Party (PRS) and Balanta ethnic group. It triggered a spate of protest calls to radio phone-in programmes by disgruntled Yala supporters.
Political analysts said many Balantas and PRS supporters would refuse to vote for Vieira, despite Yala's unexpected support for him.
Vieira came to power in a 1980 coup and ruled this West African country for 19 years until he was ousted in 1999 during a civil war. During his time in power, Vieira was widely accused of oppressing and persecuting the Balanta, who comprise 30 percent of Guinea-Bissau's 1.3 million people and form the backbone of the PRS.
Yala's fierce opposition to Vieira in the late 1990s helped sweep him to power in the 2000 presidential election, with the Balanta vote solidly behind him. Yala was overthrown by a bloodless military coup three years later.
Prime Minister Carlos Gomes Junior said his minority PAIGC government, which came to power after parliamentary elections in March 2004, would resign in protest should Vieira, 67, be elected head of state.
Reacting to the news that Yala had decided to support Vieira in the second round of the presidential election, Gomes Junior said during a visit to the nearby Cape Verde Islands: "If Nino Vieira wins the election I am going to resign because I will never co-habit with a bandit and mercenary who betrayed his own people."
The resignation of Gomes Junior's government, which controls 45 of the 100 seats in parliament, could open the way for Yala's PRS, which has 35 seats, to return to power in coalition with minority parties or even a dissident faction of the PAIGC.
Several influential PAIGC leaders were suspended from the party in May because they chose to support Vieira as a presidential candidate instead of Bacai Sanha.
Vieira has been accused of ordering the execution of several suspected political opponents during his years in power.
He has close links with President Lansana Conte of neighbouring Guinea-Conakry and has lived in exile in Portugal for the past six years.
His rapprochement with Yala marks a remarkable turnaround from the situation a few years ago when Yala was president. When Vieira at the time offered to come home and stand trial, Yala said Vieira should bring with him Paulo Correia and Viriato Pa, two Balanta army officers who were executed while he was head of state.