"East Pokot, with a population of over 300,000 people who rely on relief food, is the most affected," Osman Warfa, the Rift Valley Provincial Commissioner, told IRIN.
"It is still raining [and] almost all the roads from Chelkelgit [the district headquarters] where the food is stored are impassable.
"A number of bridges have been swept away."
This has prevented the distribution of relief food, in the past two weeks, to remote parts of East Pokot, he said.
Flash floods in Turkana further north, have made transporting aid supplies very difficult and expensive, he added. Turkana has recorded high malnutrition rates.
"Flash floods experienced in Turkana a fortnight ago left a trail of destruction. Water levels have dropped, but large trucks with heavy goods cannot access the roads in affected areas," said Moses Atuko, the Kenya Red Cross Society's North Rift regional manager.
Aid agencies there, he said, have been forced to use vehicles which can only ferry small consignments of food, increasing the cost of delivering relief.
Costs could rise further. "We are prepared to use all means, including airlifting relief food," said Warfa, the Rift Valley Commissioner.
The expected onset of the short rains in October could lead to more flooding, aggravating food insecurity, notes the UN Office for the Coordination of Humanitarian Affairs (OCHA). Some 3.75 million people in Kenya face food security, according to OCHA.
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