"Today at 2:20 pm, our nation suffered a tragic air accident... I am deeply saddened to announce the passing of General Francis Omondi Ogolla, the Chief of the Kenya Defence Forces (CDF)," Ruto told reporters.

The president, who had convened an urgent meeting of the National Security Council after news of the accident emerged, said nine other "gallant military personnel" on board were also killed while two survived.

Ogolla, 61, a trained fighter pilot, had only been in the post a year.

Ruto said the Kenya Air Force had dispatched an investigation team to establish the cause of the crash, which took place in Elgeyo Marakwet county, about 400 kilometres (250 miles) northwest of the capital Nairobi.

Ogolla's helicopter went down shortly after takeoff from the village of Chesegon, where he and his entourage had been visiting a school after making stops in other areas to see Kenyan troops and other sites.

- 'Distinguished four-star general' -

Ruto announced three days of mourning from Friday, with official flags to fly at half mast.

The bodies of the victims, draped in Kenyan flags, were returned to Nairobi on an air force plane late Thursday, according to images shared by the presidency.

"A distinguished four-star general has fallen in the course of duty and service of the country," Ruto said.

"Our motherland has lost one of her most valiant generals, gallant officers, service men and women."

Kenyan media reports said this was the fifth military chopper crash in 12 months, with claims the aircraft were old and poorly maintained.

Ruto said Ogolla had left Nairobi on Thursday morning on a "Huey" helicopter to visit troops in the North Rift area deployed as part of Operation Maliza Uhalifu (Operation End Crime in Swalihi), and other sites.

Kenyan authorities have long battled insecurity in the North Rift region, with armed bandits and cattle rustlers rampant.

The Bell UH-1B helicopter, nicknamed the "Huey," was developed in the 1950s and widely used by the US military during the Vietnam War.

- 'Significant loss to the nation' -

"The helicopter burst into flames after crashing and it had more than 10 senior commanders on board including General Ogolla," a police officer had told AFP earlier.

"They were in the area on a security mission because there are KDF (Kenya Defence Forces) soldiers deployed in the region," he added.

Ogolla was appointed Chief of the Defence Forces by Ruto in April last year after a near two-year stint as deputy.

Under Kenyan military regulations, the defence chief normally retires at 62 or after four years in the post, whichever comes first.

Ruto told journalists last May that he appointed Ogolla despite him being among those who tried to overturn his narrow election win against opposition leader Raila Odinga in 2022.

"When I looked at his CV, he was the best person to be (a) general," Ruto said, adding his decision went against the wishes of many people.

Ogolla joined the KDF in April 1984, rising through the ranks to command the Kenyan Air Force in 2018, a post he held for three years.

Ruto's predecessor Uhuru Kenyatta said Ogolla's death was a "significant loss to the nation".

"The CDF was not only an accomplished military leader, but also a devoted patriot who dedicated his life to serving and protecting our beloved country."

Workneh Gebeyehu, secretary general of the regional grouping IGAD, sent his condolences in a message on X.

"This loss is not only felt by Kenya but also by the entire region," he added.