Fiat said the value of the purchase from a trust run by the US auto union UAW to pay health care benefits for Chrysler retirees was its estimate, which still had to be determined by a US court.

In July, the Italian company said it was exercising its option to purchase another 3.3-percent tranche from the Voluntary Employee Beneficiary Association (VEBA) trust.

"Following the consummation of both purchases, Fiat will hold 65.17 percent of the outstanding equity in Chrysler," the company said in a statement.

Fiat took over operational command of the ailing US automaker in June 2009, when Chrysler emerged from a government-supported bankruptcy following a collapse in sales amid the financial crisis.

In June 2011, Fiat took a majority stake of the company and Fiat boss Sergio Marchionne is now also chief executive of the Chrysler Group, though the two groups still operate independently.

Marchionne does not foresee a full merger before 2015.