"I have heard about people saying the Islamic courts have halted their plan for jihad. This is a baseless statement - we shall never renege on our promise to fight Ethiopian invaders," he said.
Government officials could not be reached for comment on Tuesday, but Ali Jama, the government's information minister, had said the day before that government forces were on alert.
He said that dialogue could still avert a direct armed conflict.
Over the weekend, Sheikh Sharif Sheikh Ahmed, a chief ICU official, said the movement was prepared for "dialogue" with Ethiopia.
Ahmed and Sharif Hassan Sheikh Aden, the speaker of the Somali parliament, announced a deal to bring the ICU and the government back to negotiations after Arab League-mediated peace talks collapsed last month.
The government has toned down its objection to peace talks with its rival, who control swathes of southern and central Somalia, but said the ICU's rhetoric was making a search for dialogue impossible.
The ICU has already declared a jihad on Ethiopian forces and recently clashed with Addis Ababa troops.
Ethiopia has sent several hundred military trainers and advisers to help the Somali government, but denies widespread reports it has deployed thousands of combat troops to Somalia to check an ICU advance towards Baidoa, the only city held by the transitional administration.
The ICU rejected the recent UN approval of deployment of peacekeepers to protect the government. Clerics allied to the ICU vowing to attack any foreign troops stepping into the country.
Somalia has lacked an effective administration since Mohamed Siad Barre was forced from power in 1991. The two-year-old interim government has failed to keep control of the country.