* Police keep Ivory Coast opposition leaders indoors
* Opposition forms parallel government
* Standoff could flare into further violence
* Guinea opposition plans to challenge results (Adds French reaction, new death toll, attacks)
By Edward McAllister
DAKAR, Nov 3 (Reuters) - Ivory Coast opposition leaders refused to disband their breakaway government on Wednesday despite being put under effective house arrest following a disputed presidential election.
The country and its neighbour Guinea are experiencing parallel post-election crises after their presidents both decided to run for a controversial third term in office, prompting fears of prolonged instability.
The moves could spook investors and undermine democracy in a region where Islamist groups exploit discord to win recruits, analysts say.
The opposition in Ivory Coast boycotted Saturday's election and announced a rival administration after President Alassane Ouattara was declared the landslide winner. On Tuesday night police in riot gear took up positions around the homes of key opposition leaders, preventing them from leaving.
"Let's stay mobilized for the love of a reconciled Ivory Coast ... and against this autocratic regime which has flouted the Constitution," opposition leader and former president Henri Konan Bedie tweeted from his surrounded house on Wednesday.
In Guinea, dozens of people have been killed in skirmishes between security forces and protesters in the lead-up to and after the Oct. 18 election that gave President Alpha Conde an overwhelming victory. The opposition has called for more protests and challenged the results in court.
Analysts say neither result is likely to be overturned but that the standoffs could escalate in a region that has struggled to make strides towards multi-party democracy since the 1990s.
The U.S. embassy in Ivory Coast condemned the violence surrounding the election and called for calm and dialogue between the parties in a statement on Wednesday.
France's foreign ministry is aware of the announcement of Ouattara's provisional victory, a spokesperson said on Wednesday, but condemned the "serious violence" and "acts of intimidation" that have taken place.
At least 40 people have been killed before, during and after the vote, in violence that has sparked fears of a repeat of 2010 when a disputed election won by Ouattara led to a brief civil war which killed 3,000 people.
The country has a two-term limit for the presidency, as does Guinea, the top bauxite producer and home to one of the world's largest untapped iron ore deposits. But both presidents said recent constitutional changes had reset their mandates.
"The confines placed on West African leaders have been bent and we have seen a regression in democratic standards," said Eric Humphery-Smith, analyst at British-based risk consultancy Verisk Maplecroft. "It is something to be worried about."
TEAR GAS, MACHETE ATTACKS
In a sign of potential skirmishes to come in Ivory Coast, riot police fired tear gas at opposition supporters outside the homes of the opposition leaders on Tuesday after the government accused them of sedition.
In the centre of the country, where politics is frequently split along ethnic lines, local officials have confirmed post-election machete attacks, reviving memories of the civil war.
The convoy of Communications Minister Sidi Toure came under gunfire on Tuesday night in a central region, killing a member of his entourage, two government sources said.
Farmers in the cocoa belt have been afraid to tend their crops at the start of the season for fear of violence, they said, raising the risk of disease and rot. Middlemen said they are not going into the bush to buy, which could ultimately slow exports.
"Even fairly low-level police action ... will probably cause some casualties and tend to have a negative impact on investors' perceptions of risk," said South Africa-based risk consultancy firm NKC African Economics.
In Guinea, the country's biggest bauxite exporter, Société Minière de Boké (SMB), has seen some impact from the unrest, though losses have been limited, said managing director Frédéric Bouzigues, without elaborating.
"For mining companies, it is absolutely fundamental to promote a climate of peace and stability which allows us to work in peace," he said. (Reporting by Edward McAllister in Dakar, Saliou Samb in Conakry and Loucoumane Coulibaly and Ange Aboa in Abidjan Editing by Bate Felix, Philippa Fletcher and Gareth Jones)
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