The number of Kenyans in need of food aid has nearly doubled to almost four million, Kenya's government has said.
Farmers in affected areas are losing their animals
Special Programmes Minister John Munyes told AFP news agency the figure has "shot up" by at least 1m because other areas were affected by the drought.
A UK minister has pledged a further $5.3m in aid on a visit to the north-east, where many face hunger.
Meanwhile, aid agency Oxfam says "serious flaws" in food distribution networks are putting people at risk.
It says a lack of UN resources has led to the government setting up a parallel system to supply extra food.
"Instead of a united, efficient and co-ordinated response, we are left with a fractured, inefficient and wasteful system, " Oxfam's Paul Smith-Lomas says.
Last week, the BBC reported that farmers in western Kenya were ignoring an order to sell their successful maize crop to the government to help the hungry in the drought-hit parts of the country.
In December, Kenya appealed for $150m in aid to help save 2.5m threatened by the famine in the north-east.
British International Development Secretary Hilary Benn on a visit to Wajir, the area at the centre of the food shortages, announced an extra £3m ($5.3m) in emergency relief, bringing the total amount of British help to £12.7m.
"What I have seen today in this hospital in Wajir convinces me that there are unacceptable levels of severe malnutrition in Kenya and urgent action is needed by all parties," Mr Benn said, calling on other donors to come forward.
Oxfam says that an average of one child a week dies in Wajir's therapeutic feeding centre alone.
One third of the British funding will go towards transporting food, the other towards providing water.
The drought affecting Kenya has been declared a "national disaster" by President Mwai Kibaki.
The United Nations World Food Programme says aid agencies are short of cash to buy food from areas with surplus harvests.
"Without new donations, WFP will run out of food to distribute in drought affected areas by the end of February," WFP spokesman Peter Smerdon told AP news agency.
"Our previous warning and appeals have sadly received little response... we don't want Kenya to become another Niger, where in 2005 donation only increased when people started dying," he said.
The WFP has warned that 11 million people across the Horn of Africa now need food aid.
It said the number in need of urgent aid in southern Ethiopia had risen to 1.75m.