WASHINGTON (AFP) - The United States will on Thursday recognise the first Somali government in two decades, heralding a significant shift in ties since the deadly 1993 attack on US helicopters over Mogadishu.

The beginning of a new chapter will come when US Secretary of State Hillary Clinton exchanges diplomatic notes with visiting Somali President Hassan Sheikh Mohamud, a top US official said on Wednesday.

"The visit here this week of the new Somalian president Hassan Sheikh Mohamud represents a significant change in the security and political situation on the ground in Somalia and our relationship with that country," Assistant Secretary of State Johnnie Carson told journalists.

Somalia has not had an effective central government since 1991.

Two years later, Americans were shocked by scenes of US soldiers being dragged through the streets of Mogadishu after Somali militants shot down two Black Hawk helicopters. Eighteen Americans died, and 80 were wounded.

However, a new Somali administration took office last year, ending eight years of transitional rule by a corruption-riddled government.

And in recent months, a 17,000-strong African Union force, fighting alongside government troops and Ethiopian soldiers, finally wrested a string of key towns from the control of Islamist Shebab insurgents.

Mr Carson hailed recent US policies on Somalia, and praised the work of African nations through the African Union force in Somalia AMISOM, which helped oust the militants from their last stronghold in Kismayo in September.

"This has been a major, major success. We are long way from where we were on Oct 3, 1993 when Black Hawk down occurred in Mogadishu," Mr Carson said.

"Significant progress has been made in stabilizing the country and in helping to break-up and defeat al-Shebab. Much more needs to be done but we think enormous progress has been made," he added.