NAIROBI: US President Barack Obama declared Saturday that "Africa is on the move", praising the spirit of entrepreneurship at a business summit in Kenya as he kicked off a landmark visit.

Obama arrived in Kenya late on Friday, making his first visit to the country of his father's birth since he was elected president.

"I wanted to be here, because Africa is on the move, Africa is one of the fastest growing regions in the world," Obama said, drawing cheers and applause from delegates.

"People are being lifted out of poverty, incomes are up, the middle class is growing and young people like you are harnessing technology to change the way Africa is doing business," Obama said in his first official engagement in Nairobi.

The US embassy itself warned the summit could be "a target for terrorists", but Kenyan President Uhuru Kenyatta, sharing the stage with Obama, said the event showed a different side to Africa.

"The narrative of African despair is false, and indeed was never true," Kenyatta said. "Let them know that Africa is open and ready for business."

A massive security operation was under way in Nairobi, with parts of the usually traffic-clogged capital locked down and airspace also closed for the president's landing on Friday and his scheduled departure late Sunday for neighbouring Ethiopia.

Top of the list of security concerns is Somalia's Al-Qaeda affiliate, the Shebab, who have staged a string of suicide attacks, massacres and bombings on Kenyan soil. Two years ago a Shebab assault on the Westgate shopping mall in the heart of the Nairobi left 67 dead.

Obama later laid a wreath at the memorial site of the US embassy destroyed in an Al-Qaeda attack in 1998, standing in silence in memory of the 224 killed in the twin bombings in Nairobi and Tanzania.

Obama said he was delighted to be back.

"It is wonderful to be back in Kenya," Obama said, also greeting the summit with a few words of Swahili. "I'm proud to be the first US president to visit Kenya, and obviously this is personal for me. My father came from these parts."

Barack Obama Sr was a pipe-smoking economist who the US leader has admitted he "never truly" knew. He walked out when Obama was just two and died in a car crash in Nairobi in 1982, aged 46.

Excitement has been building in Kenya for weeks, with the visit seen as a major boost for the east African nation's position as a regional hub -- something that has taken a battering in recent years due to Shebab attacks and political violence that landed Kenyan leaders in the International Criminal Court.

The visit is also the first ever to Kenya by a sitting US president. At least 10,000 police officers have been deployed to the capital.

Kenyatta greeted Obama as he stepped off Air Force One late Friday. The president's half-sister Auma was also on the tarmac to welcome him and travel in the bomb-proof presidential limousine, nicknamed "The Beast", for the drive to the hotel in the city centre, where Obama dined with members of his extended Kenyan family.

Counter-terrorism will be a key topic for discussion in bilateral talks with Kenyatta on Saturday afternoon.

Kenya is now the target of frequent Shebab attacks, while the country's Muslim-majority regions are facing a major recruitment drive by the militants.

The United States is a key security partner for Kenya, which has troops in Somalia as part of the African Union force, and US drones frequently target Shebab fighters -- killing the group's previous leader last year.

A presidential visit to Kenya had been put on hold while Kenyatta faced charges of crimes against humanity for his role in 2007-08 post-election violence. The ICC has since dropped the case, citing a lack of evidence and accusing Kenya of bribing or intimidating witnesses.

Kenyatta, however, has signalled that his controversial Deputy President William Ruto, still on trial at the ICC and outspokenly homophobic -- having describing gays as "dirty" -- would be present when government officials meet Obama.

Asked earlier this week whether gay rights would be discussed, Kenyatta insisted it was "a non-issue", but Obama, in an interview with the BBC, said he was "not a fan of discrimination and bullying" and that this would be "part and parcel of the agenda".

On Sunday Obama will meet with members of Kenya's civil society, who have complained of growing restrictions in the country. He is not scheduled to visit his father's grave in the village of Kogelo in western Kenya, and bemoaned the heavy security restrictions earlier this month.

"I will be honest with you, visiting Kenya as a private citizen is probably more meaningful to me than visiting as president, because I can actually get outside of the hotel room or a conference centre," Obama said.