肯尼亚总统大选开始投票

Kenyans are casting ballots in their country's presidential election, bringing to a close yet another turbulent campaign season in the economically vital East African nation.

Voters began lining up hours before dawn Tuesday to cast their ballots in hotly contested nationwide polls. One voter, 31-year-old Mildred Malubi, said she waited in line for three and a half hours to vote in Kangemi slum, in Nairobi.

This year's election is the second consecutive election between the incumbent, 55-year-old Uhuru Kenyatta, and his longtime rival, 72-year-old Raila Odinga, who is making his fourth run for the presidency. Kenyatta has the support of Kenya's majority Kikuyu ethnic tribe, while Odinga is favored by ethnic Luo people.

The campaign has been marred by accusations of vote rigging made by Odinga against the president, and the murder of a top-ranking election official. The heightened tensions have raised concerns of a repeat of the disputed 2007 vote, when more than 1,100 were killed and 600,000 more displaced in a wave of ethnic violence.

Former U.S. President Barack Obama, whose father was born in Kenya, issued a statement Monday calling on all Kenyans to "reject violence and incitement."

"I urge all Kenyans to work for an election — and aftermath — that is peaceful and credible, reinforcing confidence in your new Constitution and the future of your country," Obama wrote.

Thousands of election observers have been deployed throughout Kenya, including former U.S. Secretary of State John Kerry.

The polls close at 5 pm local time. Results are expected by Friday.