Three Italian soldiers were killed in Afghanistan on Monday when their armoured jeep overturned in a river in Herat province as it raced to the rescue of another unit, Italy's defence ministry said.

The Italian-made Lince vehicle "flipped over in the river, trapping the soldiers inside," read the statement. It said the accident happened some 20 kilometres (12 miles) southwest of Shindand in western Afghanistan.

The soldiers -- all of them based in Shindand -- had been trying to rescue another unit "blocked by particularly adverse weather conditions."

A fourth soldier was injured in the accident and "is being treated for hypothermia. He is conscious and his life is not in danger," the ministry said.

In September 2011, three Italian soldiers involved in the training of Afghan forces were killed in a road accident that also occurred in Herat.

Italy has deployed 3,800 soldiers as part of NATO's International Security Assistance Force. A total 47 Italian soldiers have been killed or died in accidents in Afghanistan, according to an AFP calculation.

Italian Prime Minister Mario Monti said he was "pained" to hear of the accident and expressed his condolences to the families. President Giorgio Napolitano said Italy was in "deep mourning" over the deaths.