Kenya's main opposition figure, Raila Odinga, who is widely expected to stand against President Uhuru Kenyatta in an election in August, was treated in hospital for food poisoning on Wednesday.

"He was treated for normal food poisoning earlier today and he is back home," his spokesman Denis Onyango told Reuters, adding that the illness was not severe.

Odinga, 72, recently formed a new opposition coalition called NASA with three other parties.

The political alliance has yet to name its flagbearer for the coming election but Odinga is seen as a strong contender to challenge Kenyatta who is standing for the ruling Jubilee coalition.

In the same poll, voters will also pick a new parliament and regional authorities.