"We assessed battlefields, spoke to civilians, visited hospitals and areas that were affected by the clashes," he said when asked how the figure was reached.
'Worst in 15 years'
Without giving specifics Korgab said damage to property by the heavy fighting was an estimated "$1.5bn".
"The situation is Somalia has gone from bad to worse after the intervention of Ethiopian troops"
Abed, Kumasi, Ghana
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Humanitarian groups have described the clashes, most of which occurred in around the stadium area and Al Kamin neighbourhood in southern Mogadishu, as the worst in 15 years.
A local rights group, which compiled initial figures from hospitals and witnesses, said 381 civilians had died and 565 were wounded in the four days of clashes between March 29 and April 1.
Most of the dead have been buried.
The UN refugee agency (UNHCR) said around 124,000 people, mostly civilians, have fled the blood-soaked capital in the past two months as a result of the violence.
Last week, Eric van der Linden, the European Union envoy to Nairobi, said he had asked Brussels to investigate whether Ethiopian-Somali forces committed war crimes in the bloody crackdown.
Somalia has lacked an effective central government since the ousting of former dictator Mohamed Siad Barre in 1991 touched off a bloody power struggle that exploded into inter-clan warfare.
More than 14 attempts to restore a functional government in Somalia have since failed.