Somalia's former Islamic Courts Union (ICU) allies have traded tough words in public speeches and across the media in recent days, Radio Garowe reports.
Sheikh Sharif Ahmed, the current interim President of Somalia, was the ICU executive chief in 2006 alongside Sheikh Hassan Dahir Aweys, who was then the ICU's legislative head.
The two men parted ways in mid-2008, when Sheikh Sharif joined the peace process with the Somali Transitional Federal Government (TFG), then led by Col. Abdullahi Yusuf.
On Friday, Sheikh Aweys spoke at a public rally in Mogadishu for the first time since returning to Somalia after fleeing Ethiopian troops in early 2007.
"I do not recognize the government [of President Sheikh Sharif] because it is not a sovereign government and it is commanded by foreign powers," Sheikh Aweys told supporters in Mogadishu.
He spoke briefly about Islamic law, saying that he welcomed the Somali parliament's recent vote in favor of implementing as the country's national legislation.
But he had reservations about comments attributed to Prime Minister Omar Abdirashid Ali Sharmake, who said that the Islamic law in Somalia will not be similar to the Taliban of Afghanistan.
"Shari'ah [Islamic] law is necessary for this country [Somalia] but a law that requires the approval of Ethiopia and the United States will not work in this Muslim country," Sheikh Aweys added.
He demanded that African Union peacekeepers (AMISOM) withdraw from Mogadishu, warning that the armed opposition will "fight them like the Ethiopian troops."
But President Sheikh Sharif dismissed Sheikh Aweys' threats, calling him "irresponsible" on the BBC's Arabic language service.
"Sheikh Aweys has no authority to say that the Somali government is illegitimate," President Sheikh Sharif said.
He cautiously welcomed Sheikh Aweys' return to Mogadishu after spending more than two years exiled in Asmara, the capital of Eritrea.
"We will speak with anyone who can change the situation in Somalia, but we will see if Sheikh Aweys returned to wage war," the Somali President added.
Somalia has been mired in armed conflict since 1991, when the Horn of Africa country's last effective ruler was overthrown by warlords.
Rival Islamist factions control different parts of south-central Somalia, with the hardliners like Al Shabaab and Hizbul Islam rejecting President Sheikh Sharif's interim government.