Ahmed, who is seen as the best hope of restoring stability to Somalia, said that progress could only be made if order was returned to the country.
"We are firmly determined to undertake reforms ... to try to alleviate the suffering of the Somali people," he said.
Somalia, which has suffered from unrest since 1991, is trying to restore calm under a transitional government led by Ahmed, which aims to assert authority over opposition fighters in the southern and central regions.
But in a politically significant development, Sheikh Hassan Dahir Aweys, a prominent opposition figure, returned to Somalia after spending two years in neighbouring Eritrea.
Aweys, who is on the US list of "terrorism suspects" for his alleged links to al-Qaeda, arrived in Mogadishu, Somalia's main city, on Thursday, according to Hizbul Islam, an umbrella group of four organisations, including the one that Aweys heads.
Aweys, head of the Islamic Courts Union, which took control of large parts of the country in its battle against the transitional government, still wields significant influence over some fighters.
More than one million people have been uprooted by fighting in the past two years and one-third of the population survives on food aid.
Somalia has also been the home ground for a wave of piracy attacks on ships in the Gulf of Aden and Indian Ocean, which has driven up insurance rates and other costs in sea lanes linking Europe to Asia.
In his speech at Thursday's Brussels conference, Ban called piracy "a symptom of anarchy and insecurity on the ground".
He said "more security on the ground will make less piracy on the seas".