The UN envoy to Somalia has urged the country not to waste "the best opportunity for peace for 16 years" after visiting the president.
Francois Fall (l) said it was important to see President Yusuf in the capital
Francois Fall urged President Abdullahi Yusuf to set up an inclusive government following the ousting of an Islamist group from the capital, Mogadishu.
Meanwhile, the sacked speaker of parliament has said he fears Mr Yusuf could become a dictator.
Sharif Hassan Sheikh Adan was impeached after several rows with the president.
A new spokesman for the Union of Islamic Courts (UIC) has told the BBC there will be "unprecedented war" in Somalia unless Ethiopian forces withdraw.
Sheikh Mustafa, speaking from Somalia, said the Islamists wanted reconciliation and dialogue.
The Somali government has estimated there are some 3,000 Islamist fighters in Mogadishu but the location of their leaders is not known.
Mr Fall, surrounded by tight security as he arrived in Mogadishu, held talks with President Yusuf concerning the plans to send an African peacekeeping force to Somalia, to replace the Ethiopian troops who helped drive out the UIC.
8,000-strong force proposed
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Mr Yusuf arrived in Mogadishu last week for the first time since being elected president at peace talks in 2004.
Somalia has not had a functioning national government since Siad Barre was toppled in 1991.
"I want to congratulate you. To see the president in Villa Somalia [the presidential palace] is a very important step," Mr Fall told the president.
"There has been a lot of crime, a lot of devastation, but if you look back and say: 'This man killed my son or husband,' you will never be reconciled in this country," the envoy said.
'Rule by force'
The US has also urged reconciliation in Somalia and said the vote by MPs to impeach the speaker of parliament was likely to have a negative impact on dialogue.
Mr Adan was sacked for holding unauthorised talks with the Islamists while they controlled much of southern Somalia last year.
"There is a dictatorship risk and some of the elements are already in place, such as the emergency legislation [passed by parliament last weekend]," he told Reuters news agency in Rome.
"The president believes he can rule by force... He will try to rule the country alone, with the help of Ethiopian troops," he warned.
Mr Adan had fallen out with both the interim president and the prime minister.
"The symbol of the president and the prime minister combining to push him out is counter to that spirit of reconciliation," US assistant secretary of state for African affairs Jendayi Frazer said.
The Ethiopians say they want to leave Somalia by the end of the month and regional diplomats are trying to muster enough troops for an 8,000-strong African force for Somalia.
So far only Uganda has agreed to provide peacekeepers.
On Tuesday, the leaders of Ethiopia and Kenya said several unnamed African countries had offered to contribute troops to the force.
Mr Adan had a series of rows with President Yusuf
Both South Africa and Tanzania have said it is too early to decide whether they will contribute troops to the proposed African peacekeeping force.
Nigeria and Uganda are set to discuss the issue at the end of the month and BBC African analyst Martin Plaut says it would take weeks for any troops to be deployed.
He says that if the Ethiopian forces withdraw before peacekeepers arrive, that could result in a dangerous power vacuum.