Carson, assistant secretary for African affairs, was in Mogadishu Sunday for a visit that would have been unthinkable just a year ago due to security concerns, CNN reported.
"I think that we probably are in the best position that we have been in more than two decades, and my very presence in Mogadishu was an acknowledgment of the progress made," Carson told CNN.
Security has improved in Mogadishu since the African Union pushed the militant group al-Shabaab out earlier this year but political reforms must keep pace, Carson said.
The mandate for Somalia's transitional government expires in August. A new constitution must be passed and new leaders elected before then, CNN reported.
Carson, who met with Sheik Sharif Sheik Ahmed, president of Somalia's transitional government, as well as other high-ranking officials, said al-Shabaab represents a significant terror threat.
"Over the last year, al-Shabaab has become formally affiliated with al-Qaida, and senior leaders of al-Shabaab have befriended individuals who are linked with al-Qaida," he said.
"They have befriended foreign fighters who have come in from the Middle East and South Asia. And their presence is a source of concern in Somalia as well as in the region and also for the global community."