COTONOU (Reuters) - Benin authorities arrested the niece and personal doctor of President Boni Yayi, claiming they had tried to poison him at the behest of an angered businessman, the country's state prosecutor said.

Doctor Ibrahim Mama Cisse, the president's niece Zouberath Kora, and former trade minister Soumanou Moudjaidou were arrested on Sunday, while cotton magnate Patrice Talon - the suspected ringleader of the poison plot - is on the run, Justin Gbenameto told reporters late on Monday.

"The prosecution has requested that they should be charged with conspiracy and attempted murder," Gbenameto said, adding the attempt to poison Yayi occurred on October 17 while he was visiting Brussels.

Gbenameto said Moudjaidou is believed to have brought the poison into the country, where he gave it to Cisse to be switched with his regular medication. Kora was meant to have administered it, but the plot was discovered after she told a family member about the plan, he said.

Talon - who lost a lucrative port and customs reform contract in the cotton exporting country earlier this year - offered $2 million each to Cisse, Kora and Moudjaidou for their roles, Gbenameto said.

Yayi, 60, a former banker, became president in 2006 and survived an assassination attempt in 2007 when gunmen ambushed his convoy. He won re-election in March last year following a disputed presidential election.

(Reporting by Samuel Elijah; Writing by Bate Felix; Editing by Richard Valdmanis and Jon Hemming)