She is expected to endorse Somalia's beleaguered transitional government amid fears the country is becoming a haven for Islamist militants.
Large swathes of Somalia are out of the government's control.
With the al-Shabab rebels growing in strength, more than 250,000 people have fled their homes over three months.
Mrs Clinton will hold talks with the UN-backed Somali leader on the second day of her African tour.
Somali Foreign Minister Muhammad Abdullahi Omar told the BBC the US was "seriously engaged" in helping bring stability and peace to his country.
Wreath-layingBefore Thursday's meeting, she will honour the victims of the August 1998 attacks（攻击） on the US embassies in Kenya and Tanzania, in a wreath-laying ceremony in Nairobi.
It [al-Shabab] poses a threat to Kenya, poses a threat to the stability of Africa and beyondHillary ClintonUS secretary of stateMeeting Somalia's al-ShababQ&A: Somalia's conflictIn pictures: Somali refugee cityPresident Ahmed needs all the support he can get, says the BBC's Will Ross in Nairobi. Pro-government forces are only in control of a small section of the capital Mogadishu.
There are reports that al-Shabab - which favours strict Islamic law - is gaining support from extremists around the world, our correspondent says.
Earlier this week, police in Australia arrested several men, charging them with planning suicide attacks on a base in Sydney and saying they were linked to al-Shabab.
Our correspondent points out it is far too dangerous for the American secretary of state to venture into Somalia, as the fighting continues.
Speaking on the sidelines of an economic summit on Wednesday, Mrs Clinton said: "We know we're facing a very difficult conflict（冲突）, and we also know that the presence of al-Shabab and terrorist elements within Somalia poses a threat," reports Reuters news agency.
"It poses a threat to Kenya, poses a threat to the stability of Africa and beyond. So this is an area where we're going to work even more closely together."Somalia's foreign minister told the BBC's Network Africa programme that Washington's support for his government was a "golden opportunity".
"It is absolutely clear that the people of Somalia are tired... sick and tired of war, sick and tired of chaos," he said.
"We believe we have reached a critical stage where we hope to build momentum and mass to enable us to get to the next stage of stabilising the capital and the surrounding regions and then to move on."The US admits it has supplied pro-government forces in Somalia with over 40 tonnes of weapons and ammunition this year, and another delivery of weapons is predicted, says our correspondent.
But there are growing fears that the Horn of Africa country - which has been without an effective central government since 1991 - risks becoming a haven for terrorists.
'Enormous potential'
On Wednesday, Mrs Clinton held talks in Nairobi with Kenya's president and prime minister.
CLINTON'S AFRICAN TOURKenyaSouth AfricaNigeriaAngolaLiberiaDemocratic Republic of CongoCape VerdeSend us your commentsAmerica's top diplomat described as "disappointing" Kenya's failure to investigate a bout of violence that left at least 1,300 people dead after the disputed December 2007 presidential election.
Addressing African leaders at Wednesday's economic summit, Mrs Clinton said the continent had "enormous potential for progress".
But she stressed that harnessing that potential would require democracy and good governance.
During her 11-day trip Mrs Clinton will also visit South Africa, Nigeria, Angola, Liberia, the Democratic Republic of Congo and Cape Verde.(本文由在线英语听力室整理编辑) |