The attacks, which also wounded more than 80 people, ripped through a rally in Nairobi of people campaigning against a proposed constitution to be submitted to a referendum.
"The president has convened an early morning security meeting to discuss this matter in order to get to the bottom of this matter," Vice-President Kalonzo Musyoka said.
"We are appealing for calm from all Kenyans as police investigate," he said.
The blasts went off late on Sunday during a rally to oppose the proposed constitution, held in the capital's main park.
Yesterday, police were still combing the park for clues.
Authorities said on Sunday that five people had died, but police said yesterday that they had found a sixth body, that of a 51-year-old man with shrapnel wounds, in a car next to the park.
The emergency meeting was due to be attended by the president, by Prime Minister Raila Odinga, by the ministers of the interior and of defence, and by the country's army chief.
A referendum is due to be held on August 4 on the proposed constitution, which was one of the main reforms pledged by Kenya's leaders in the aftermath of the deadly violence sparked by the disputed 2007 election.
Sunday's blasts were the worst incident of its kind since the police and tribal violence that killed 1500, displaced hundreds of thousands and tainted Kenya's image as the region's most stable nation.
Though Kenya's once feuding principals publicly support the new constitution, their parties appear to be divided, with some politicians concerned about land issues and a clause on legalising abortion if it is necessary to save the life of the woman.
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