"We will reconsider taking part ... due to the US military attack," he
said in a telephone interview from Cairo on Friday.
The alliance, which was formed in 2007 after the Islamic Courts Union was forced from the country by Ethiopian troops and Somali transitional government forces, contains both moderates and hardliners.
Its participation is seen as being crucial to the success of the talks, which are scheduled to take place in neighbouring Djibouti.
Aden Hashi Ayro, the leader of the al-Shabaab group, was killed after a US military strike on his home in the central Somali town of Dusamareeb on Thursday.
The attack also killed another 24 people, five in the targeted house and the rest in nearby homes, witnesses said.
Members of his group have been blamed for recent attacks on transitional government troops and their Ethiopian allies in the capital Mogadishu and other towns.
However, analysts say that the air raid, the latest in a series of US military attacks in Somalia this year, is unlikely to significantly weaken the armed opposition.
Sheik Muqtar Robow, a spokesman for the al-Shabaab group, said on Friday: "This will not deter us from prosecuting our holy war against Allah's enemy."
"If Ayro is dead those he trained are still in place and ready to avenge against the enemy of Allah.
"It is impossible to hit missiles on our people and we let your citizens come to our country. We warn them to stay out of our country," Robow said.
Al-Shabaab, labelled a terrorist organisation by Washington, has concentrated on hit-and-run attacks on Ethiopian troops, killed government troops and seized weapons.
It is believed to have up to 7,000 mostly young fighters organised in several hundreds cells.
Al-Shabaab was formerly the armed wing of the Council of Islamic Courts movement which seized control of much of southern Somalia, including the capital, Mogadishu, in 2006.