Kenyan police say the half-brother of President Barack Obama has been arrested for alleged possession of marijuana.

Area police chief Joshua Omokulongolo told the Associated Press George Obama was picked up today and was being held at the Huruma police post in the capital. Omokulongolo said officers found one joint of marijuana on him. "He is not a drug peddler ... But it's illegal, it's a banned substance," Omokulongolo said.

He is due to appear in court on Monday morning.

George Obama and the president had the same father, who died in a car crash in 1982, but barely know each other.

CNN said George Obama, speaking from behind bars at the jail where he was being held, denied the allegations.

"They took me from my home," he told a correspondent for the network. "I don't know why they are charging me."

George Obama is the youngest child of Barack Senior, the Kenyan economist who was briefly married to the president's mother, Ann Dunham, while living in Hawaii as an overseas student.

George, aged 25, was tracked down last year by the Italian edition of Vanity Fair living in a 6ft by 9ft shack on the outskirts of Nairobi. He told the magazine that he was so ashamed of his impoverished circumstances, living on less than a dollar a month, that he never mentions the fact that his half-brother could soon become the most powerful person on earth.

However, he later told the Associated Press: "I'm proud of how I live.... (The media) are tarnishing the family name."

He also said he was studying to be a mechanic and works with a local youth group in Huruma.

Several of President Obama's Kenyan relatives went to Washington DC, for his inauguration, but George was not among them.

In President Obama's book "Dreams From My Father," he describes George Obama as "a handsome, roundheaded boy with a wary gaze."