At least 10 Afghan civilians were also killed in Thursday's blast on a road linking Kabul's international airport to the US embassy.
Fifty people were injured, according to Afghan officials.
"This is an unhappy day for Italy," Berlusconi told reporters.
|The blast in the Afghan capital on Thursday killed at least 16 people [Reuters]
The presence of Italian troops in Afghanistan has become increasingly controversial in Italy and has put pressure on Berlusconi's governing right-wing coalition.
Al Jazeera's Zeina Khodr, reporting from Kabul, said the Taliban claimed responsibility for the attack.
"[They said] the purpose is to show that there is nowhere safe in Afghanistan.
"The situation is deteriorating, with violence really at an all time high. As violence continues people are concerned about the security situation and the political uncertainty in this country."
Our correspondent said Thursday's blast marked the fourth major attack in the capital in five weeks.