Pope Francis said on Wednesday he wanted to offer "spiritual and material" support on his first tour of Africa, where he will address a fast-growing Catholic congregation and seek to heal divisions between Christians and Muslims.

The pope arrives in Kenya later on Wednesday before travelling to Uganda, another nation targeted by Islamist militant attacks. After that he visits the Central African Republic, a country torn apart by Muslim-Christian strife.

"I am going with joy to Kenya, Uganda and the brothers of the Central African Republic," he told reporters aboard his flight to Nairobi. "Let's hope this trip brings better fruit, both spiritual and material."

Millions of Christians - Catholics and others - are expected to turn out for public celebrations of Mass, presenting a challenge for national security forces to keep the pontiff and the huge crowds safe.

Kenya has been the target of a spate of attacks by Somalia's Islamist group al Shabaab in the past two years that have killed hundreds of people. In 2013, an assault by al Shabaab gunmen on a Nairobi shopping mall killed 67 people.

HALF A BILLION AFRICAN CATHOLICS BY 2050

Potentially the most hazardous stop may be the third leg of the trip to the Central African Republic. Dozens of people have been killed there since September in violence between mostly Muslim Seleka rebels and Christian anti-balaka militias.

Asked if he was nervous, the pope brushed off concerns about the trip with a joke: "To tell you the truth, the only thing I'm concerned about is the mosquitoes. Did you bring your spray?"

Africa's Catholic church is growing fast with an estimated 200 million adherents in 2012, a figure expected to reach half a billion in 2050. About 30 percent of Kenya's 45 million people are baptised Catholics, including President Uhuru Kenyatta.

He will address the faithful in a public Mass at Nairobi University on Thursday - declared a national holiday - and is expected to seek to heal ethnic rifts that have long plagued Kenya.

"We are living at a time when religious believers, and persons of goodwill everywhere are called to foster mutual understanding and respect, and to support each other as members of our one human family," the pope said in a pre-trip message.

Kenyan media has said at least 10,000 police will deployed in the capital for the Kenya leg, which includes a visit to the regional U.N. headquarters in Nairobi where the pope is expected to address climate issues.

In Uganda, where police said they would deploy 12,000 officers for the visit, the pope holds Mass on Saturday and then addresses young people on a continent that has a big youth belt.

In the Central African Republic, he will visit a mosque in one of the most dangerous districts of the capital Bangui.

French officials have hinted heavily that the Vatican should consider scrapping the Bangui leg of his trip or at least scale it back.