He said by telephone from Nairobi: "If the Somali government is ready to negotiate with an open mind then these negotiations can succeed.
"But if the government remains with this hard line, then nothing can be done."
Ahmed, who is the head of the Union of Islamic Courts' executive council, said he had met US officials several times and the US ambassador had helped transfer other leaders to Kenya.
Diplomats have expressed hopes that Ahmed, widely seen as a moderate in the group that controlled much of central and southern Somalia for six months from last June, could be useful in uniting the various factions in the country.
Michael Ranneberger, the US ambassador whose brief includes Somalia, first met with him in Nairobi last year in a bid to press moderation on the movement.
Ahmed said his movement remained an essential part of any dialogue because it had been "formed with the support of more than 95 per cent of the people" and "remained present on the ground in Somalia and abroad".
He turned himself over to Kenyan forces at a border crossing on January 21 and is being held at a Nairobi hotel.
Ahmed told Al Jazeera that he hoped to "leave Kenya soon" and had been in contact with Sudanese and Yemeni authorities about the possibility of moving there.
The senior Islamic courts leader's interview to Al Jazeera came against a backdrop of fresh violence in the Somali capital, Mogadishu.
An explosion at an Islamic school for women and girls killed a student on Friday. Six other students were wounded in the attack on Umu-A'isha religious school for women and girls in southern Mogadishu, witnesses said.
It happened shortly before lunchtime at the school where 110 women and girls are enrolled.
The explosion may have been caused by a mortar and the attackers were unknown.
Overnight, unknown fighters launched at least three mortars, killing at least eight people and injured 20 in Mogadishu.
The attacks targeted the seaport, a hotel and an Ethiopian military base.
Meanwhile, Kenyan authorities are reported to be preparing to deport more foreigners believed to have fought for the Islamic courts, including an American wanted in the US for links to radical movements.
Among the foreigners are four Britons, a Frenchman, a Tunisian woman, Syrians and other Arab fighters.
To date Kenya has deported at least 34 to Somalia, including people who hold Canadian, Eritrean and Kenyan passports.