Officials say George Saitoti and his deputy, Orwa Ojode, have been killed when the aircraft went down west of Nairobi, bursting into flames as it hit the ground.
There is no word on the cause of the crash, in which six people were killed, including bodyguards and pilots.
George Saitoti, 66, a former vice-president, had been planning to run in a forthcoming presidential poll.
He was on his way to a security meeting when his helicopter crashed on Sunday morning.
An AFP agency news journalist saw six charred bodies being removed from the wreckage.
Another reporter at the scene says debris of the burnt-out police helicopter were strewn in the brush.
George Saitoti had been a key figure in Kenyan politics, holding a number of senior ministerial posts over the last 30 years.
The professor of mathematics joined Daniel Arap Moi’s government as a finance minister in 1983, going on to become his vice-president in 1988.
He briefly stepped down as education minister in 1996 over accusations he was involved in the Goldenberg financial scandal, but was reinstated when a Kenyan court ruled he should not be charged.
After years as a senior member in the long-dominant Kanu party, George Saitoti joined the current president Mwai Kibaki’s National Alliance of Kenya in 2002.
As Internal Security Minister under Mwai Kibaki, he was a leading government voice against the Somali militant group al-Shabab.
Kenyan troops have been fighting al-Shabab in Somalia since they sent troops into the country last October.
The militants have killed several people in a string of grenade attacks in various parts of Kenya, including Nairobi.
George Saitoti announced he would stand for the presidency last November.
No date for the presidential election has so far been set. Mwai Kibaki’s mandate ends in January 2013.
Prime Minister Raila Odinga – a rival of both Mwai Kibaki and George Saitoti – has also announced he was standing for president.
The last presidential election, in December 2007, was followed by a wave of ethnic and political violence in which about 1,500 were killed.
Raila Odinga has warned about the emergence of ethnically-based political groups in the run-up to the next poll.
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