Somalia's interim President Abdullahi Yusuf is being treated for respiratory problems and is not in danger, officials say.
President Yusuf had a liver transplant in the 1990s
His spokesman Hussein Mohammed Mohamoud told the BBC Mr Yusuf was admitted to a Nairobi hospital with bronchitis.
Meanwhile, an Islamist leader has rejected the prime minister's offer of talks, unless Ethiopian troops leave.
Mr Yusuf's Ethiopia-backed government is battling Islamist insurgents. The UN says one million people are homeless.
The government has also lifted the restrictions it had imposed on the delivery of aid to the Lower Shabelle region, which had prompted concern among aid workers.
The government had blocked two World Food Programme ships in the port of Marka.
The ships had been escorted by the French navy to deter pirates but had been barred from unloading their food aid.
Mr Mohamoud accused the media of exaggerating the president's health problems.
President Yusuf, 72, had a liver transplant in the 1990s and has not been in good health but his spokesman said his condition was not related to his liver.
"The president is well and not in any danger as reported by the media, he is responding well to treatment and will be out of hospital soon. It is normal for anybody to be sick," Mr Mohamoud told the BBC News website.
Some health officials had described his condition as "serious".
He is due to travel to London this week, for what his aides are calling a "routine check-up".
Officials at the Nairobi Hospital where President Yusuf has been admitted have barred reporters from visiting the private ward.
But the Somali envoy in Kenya, Mohammed Nur Ali, said they plan to give a briefing to the media on his health condition.
President Yusuf will miss Wednesday's meeting of regional leaders with US Secretary of State Condoleezza Rice in Ethiopia.
Somalia is instead represented by Prime Minister Nur Hassan Hussein who was appointed just last month.
He has called for talks with the opposition leaders, hoping to end the year-long insurgency against the Ethiopian-backed transitional government, that has left at least 6,000 people dead.
Some one million Somalis are living rough, the UN says
But Sheikh Sharif Ahmed, chairman of the opposition Alliance For the Re-Liberation of Somalia (ARS), insists talks can not take place unless Ethiopia withdraws its troops from Somalia.
"Our problem is not with the old prime minister or the new one, our problem is Ethiopia's occupation," he told Reuters news agency.
Ethiopia helped the transitional government end the Union of Islamic Courts' (UIC) six-month rule over large parts of southern Somalia, last December.
Mr Ahmed was one of the UIC leaders.
On Monday, UN humanitarian affairs chief John Holmes said the international response to the situation in Somalia has been inadequate.
"This is obviously a very serious humanitarian situation in Somalia," he said.
Somalia has not had a functioning national government since 1991.