Sheikh Hassan Dahir Aweys, a top Islamist in Somalia, has arrived in the capital Mogadishu amid reports of a split in the al-Shabab group.
He was flown from the northern town of Adado, escorted by government security forces, but it is unclear whether he has surrendered or defected.
The UN says he gave himself up to government allies after infighting but clan elders deny this.
Sheikh Hassan Dahir Aweys is considered a terrorist by the UN and the United States.
Regarded as the elder statesman of Somali Islamists, he has been on a US list of people “linked to terrorism” since shortly after the 9/11 attacks in 2001.
A new UN-backed government in Mogadishu is trying to regain control of the country from al-Shabab after more than 20 years of conflict.
Supported by some 18,000 African Union soldiers, President Hassan Sheikh Mohamud’s administration is the first in more than two decades to be recognized by the US and the International Monetary Fund.
Sheikh Hassan Dahir Aweys was flown by plane from Adado, a town about 310 miles north of the capital.
“If he renounces violence, then we can start the discussion about the options available,” government spokesman Abdirahman Omar Osman told Reuters news agency, without describing the options.
Sheikh Hassan Dahir Aweys left al-Shabab territory after factions within the al-Qaeda linked group clashed last week – the first deadly infighting since it launched an insurgency in 2006.
Al-Shabab, which means “The Youth”, is fighting to create an Islamic state in Somalia – and despite being pushed out of key cities in the past two years still remains in control of smaller towns and large swathes of the countryside.
It was as a radical offshoot of the now-defunct Union of Islamic Courts, which was led by Sheikh Hassan Dahir Aweys and for much of that year controlled Mogadishu and many southern and central areas.
The exact cause of the al-Shabab split is not known, but there has been a long-running internal power struggle between its leader Ahmed Abdi Godane and those seen as more moderate who oppose links with al-Qaeda, analysts say.
There are conflicting reports about the fate of the second-in-command – Ibrahim Afghan, the al-Shabab founder – following last week’s fighting.
Initially, sources said he had been captured and was in al-Shabab detention; subsequent reports in local media say he has been executed.