One of the leaders of the main clan in Somalia's capital, Mogadishu, says he will not be taking part in the forthcoming reconciliation conference.
Ethiopia says it will pull its troops out once peace takes hold
The Hawiye clan has been opposed to the presence in Somalia of Ethiopian troops who helped government forces oust an Islamist group in December last year.
Meanwhile, a leader of the ousted Islamists says no conference can take place until Ethiopian troops withdraw.
Sheikh Sharif Sheikh Ahmed also called for an independent mediator.
Hawiye elders agreed to a ceasefire in April after the worst violence the capital had seen in 16 years.
Some 1,600 Ugandan troops are in the city, the first contingent of a proposed 8,000 strong African Union force.
Haji Abdi Iman, chairman of Hawiye elders' committee, told the BBC's Somali Service that it was wrong to insist that the conference be organised around clan allegiances.
He said Somalia's problems were political, not clan-based.
His comments add to growing uncertainty about the plans to hold the national reconciliation conference planned for the 14 June.
Issa Haji Omar of Mogadishu's Banadir University said the conference cannot go ahead without the Hawiye.
"[It] is one of the largest clans in Somalia. Second, it dominates the capital, where the government is struggling to assert full control," he told AP news agency.
Mr Ahmed, who has formed an alliance opposed to Ethiopia with former Deputy Prime Minister Hussein Aideed, said "some very important steps" needed to be taken before talks went ahead.
Ethiopian troops should leave SomaliaAn appropriate place must be chosen for talksA neutral party to mediate and bring the reconciliation to a successful conclusion.
"If these simple steps, which any person who wants the good of Somalia, are taken we are ready to negotiate," Mr Ahmed told Al-Jazeera.
Last week, Ethiopia's prime minister pledged to withdraw his troops from Somalia once peace took hold in the capital.