NAIROBI, Kenya — The head of Kenya’s electoral commission announced on Monday that William Ruto, the country’s vice president, had won the presidential election. But the validity of the result was thrown into doubt because of a statement minutes earlier by a majority of the election commissioners that they could not stand by the outcome.

In a speech just after the announcement, Mr. Ruto said: “All sovereign power belongs to the people of Kenya. I want to thank God for getting us to this point. I want to thank God that today we have concluded this election.”

He described the vote as “a very historic, democratic occasion that moves our country to the next level.”

“I know many are wondering, especially those who have done many things against us, I want to tell them they have nothing to fear,” he added. “There is no room for vengeance, there is no room for looking back, we are looking to the future.”

The election pitted two of the country’s political heavyweights against one another: Mr. Ruto is the country’s vice president, while Raila Odinga, a veteran opposition leader, has lost four previous election runs.

Kenya is East Africa’s biggest economy, and it is pivotal not only for the stability of the region, but as a hub for trade and security. The presidential race, Kenya’s closest since the country’s first truly competitive election 20 years ago, is also being closely scrutinized by Western and regional allies as a key test for democracy in one of Africa’s powerhouse nations.

Mr. Ruto, 55, also a wealthy businessman, cast himself as champion of Kenya’s “hustler nation” — the disillusioned, mostly young strivers struggling to gain a foothold.

A vice chairwoman of the Independent Electoral and Boundaries Commission, Juliana Cherera, speaking on behalf of four of the country’s seven commissioners said the panel could not take ownership of the results because of the “opaque nature” of the election’s handling.

The statement by the vice-chairman of the Independent Electoral and Boundaries Commission came on an afternoon of rising tension. The vote took place last Tuesday, and vote counting, announced both by the election commission and by media organizations, had signaled a cliffhanger.

Abdi Latif Dahir contributed reporting from Eldoret, Kenya.

Declan Walsh reported from Nairobi, and Abdi Latif Dahir from Eldoret, Kenya.