Prime Minister Raila Odinga's spokesman said Odinga had been informed of the deaths of Saitoti and his deputy, Orwa Ojode.
A former long-serving vice president under the former President Daniel Arap Moi, Saitoti was also a presidential candidate in an election expected to be held by March next year.
A Reuters photographer counted three charred bodies at the scene of the crash in a forest in the Ngong area just outside of Nairobi.
Debris of the burnt-out blue police helicopter were strewn in the brush where government officials and curious locals jostled to catch a glimpse.
It was not immediately clear what caused the crash. More people were feared to have been on board the helicopter.
Saitoti, an ally of President Mwai Kibaki, was the leading government voice against Somali militants al Shabaab, often visiting the scenes of grenade attacks inside Kenya and vowing the east African nation would crush the group.
Kenya's troops have been fighting al Shabaab in neighboring Somalia since last October. The militants have killed several people in a string of grenade attacks in Nairobi, the far north and the coast in retaliation to Kenya's moves against them.
Elsewhere in Peru, rescue specialists on Saturday reached a helicopter that crashed in the southeastern Andes, and there were no survivors among the 14 people on aboard, including eight South Koreans and three Europeans, Peruvian police said.
A police commander who went to the crash site, Raul Aybar, told The Associated Press that the aircraft “crashed into the snowy Mama Rosa and exploded.”
“Everyone died in the initial impact because everything is burned and scattered,” Aybar said after returning to the nearest city, Ocongate.
Another member of the police rescue team, Brig. Roberto Larrea, also told the AP that no one survived.
Aybar said operations at the crash site had been suspended until Sunday because of bad weather and darkness. He said temperatures had dropped to minus-15 Celsius (5 degrees Fahrenheit).
Authorities said the crashed Sikorsky S-58ET was found at an attitude of roughly 16,000 feet (4,900 meters).
Police said a Dutchman, a Czech, a Swede, eight Koreans and three Peruvians, including the pilot and co-pilot, were on the helicopter.