Somalia's transitional government has dismissed as irrelevant an agreement struck between a group of Somali MPs and the Union of Islamic Courts.
Mr Adan (R) appears at odds with the government on several issues
Spokesman Abdirahman Dinari said the MPs - led by parliament speaker Sharif Hassan Sheikh Adan - did not have a mandate to negotiate.
The MPs went to Mogadishu a week ago after Arab League mediation efforts in the Sudanese capital Khartoum failed.
The seven-point agreement called on both sides to agree to return to talks.
It also pledged to maintain an arms embargo and prevent any foreign interference in Somalia.
However, the transitional government - which has little influence outside the town of Baidoa where it is based - has called for the arms embargo to be lifted and for a foreign peacekeeping force to protect it.
The Islamists have taken control of most of southern Somalia since seizing the capital, Mogadishu, in June.
The deal was struck late on Friday in Mogadishu. The government responded after a cabinet meeting the next day.
"The government does not accept this initiative," Mr Dinari told the Associated Press news agency. "It is totally unacceptable."
"Reconciliation is the task of the government," he added.
The deal is an attempt to prevent war between militias loyal to the Union of Islamic Courts and the fragile government.
Ibrahim Hassan Adow, the Islamic Courts spokesman for foreign affairs, said: "This is a first step, and we are headed for peace."
The two parties called on the transitional government to back the deal.
Somalia has been in the grip of warlords and militias for years and has not had a functioning national government since 1991.