* Pro-Gbagbo youth groups killing West African immigrants
* Pro-Ouattara fighters execute prisoners
By Tim Cocks
ABIDJAN, March 16 (Reuters) - Security forces and militias loyal to Ivory Coast's Laurent Gbagbo have committed atrocities on an organised scale that may constitute war crimes, Human Rights Watch said.
These acts include rape, executions and burning West African immigrants to death, the monitoring group said in a report released late on Tuesday.
"It's an organised pattern of attacks on West Africans," HRW researcher Corinne Dufka told Reuters.
The world's top cocoa grower has been locked in violent turmoil since a disputed November election between Gbagbo and his rival Alassane Ouattara, widely recognised as the winner.
The HRW report lambasted gunmen claiming allegiance to Ouattara -- who have taken over parts of north Abidjan in the past three weeks -- for summary executions of 11 pro-Gbagbo troops captured since they rose up against the incumbent.
Neither side was immediately available for comment.
The report said Gbagbo's "Young Patriots", often armed youths who have set up roadblocks, had carried out a series of ethnically motivated killings since a call by their leader Charles Ble Goude to fight the rebellion late last month.
Goude was not immediately available for comment.
The report documented several cases of killings of West African immigrants and members of Ouattara's Dioula tribe by armed pro-Gbagbo youths. Immigrants often have been targeted in times of crisis since a 2002-3 war divided the country in two.
"Residents from Mali, Burkina Faso, Nigeria, and Niger gave detailed accounts of daily attacks by pro-Gbagbo security forces and armed militias, who beat foreign residents to death with bricks, clubs, and sticks, or doused them with gas and burned them alive," the report said.
ABUSES ON OUATTARA'S SIDE
Around 400 people have been killed since the election, the United Nations says, and HRW added that "the vast majority (were) killed by pro-Gbagbo forces in circumstances not connected with armed conflict and with no apparent provocation."
The widespread and systematic nature of the attacks makes them candidates for war crimes charges, the report said.
"On the Ouattara side, armed fighters have begun a pattern of extrajudicial executions against alleged pro-Gbagbo combatants detained in Ouattara territory," it said.
Though the killing of civilians by Gbabgo's forces was more systematic, the report said Ouattara's fighters had raided a village seen as pro-Gbagbo this month and killed nine people.
Ouattara's rival administration has sought to distance itself from gunmen fighting in his name, but Dufka said he still could be held accountable. "These groups have sort of emerged spontaneously, but that doesn't mean (Ouattara's government) can't pass down orders like not executing prisoners," she said.
(Editing by Michael Roddy)