Kipkalya Kones, 56, was planning to campaign in by-elections
Two Kenyan ministers were among four people killed in a plane crash near the Maasai Mara game reserve, President Mwai Kibaki has said.
Roads Minister Kipkalya Kones and Assistant Home Affairs Minister Lorna Laboso died in the light aircraft crash, he said in a statement.
Mr Kones was appointed to the cabinet as part of a power-sharing deal after disputed elections last December.
Weather conditions were reportedly poor at the time of the crash.
"Our country has lost leaders of immense potential at their prime age and with a promising future," said Mr Kibaki.
"Let us all remain united at this moment of sorrow as a nation."
A pilot and a security guard were also on board the Cessna aircraft when it crashed near the western town of Narok, Kenyan police told the BBC.
Contact with the plane was lost less than an hour after it took off from Wilson airport in Nairobi, says the BBC's Adam Mynott in the Kenyan capital.
Both ministers were members of Prime Minister Raila Odinga's Orange Democratic Movement, which is in a coalition government with Mr Kibaki's Party of National Unity.
Mr Odinga's spokesman, Salim Lone, called it "unbearable news".
The MPs had been travelling to Kenya's Rift Valley region to support candidates in by-elections on Wednesday.
In 2006, four MPs died when a military plane crashed attempting to land during bad weather.
Three years earlier, a cabinet minister died in a plane crash in western Kenya.