David Dixon, 53, who was missing since Tuesday's bombings, has been confirmed dead by his family.
Tuesday's attacks on the Brussels airport and metro system killed 31 people and injured many more.
John Kerry vowed the international community would not be intimidated by extremist attacks and will continue to fight against their "nihilistic beliefs" until they are "eliminated".
The US Secretary of State was speaking in Brussels today discussing Tuesday's attacks in the city with Belgium's prime minister.
Mr Kerry offered America's condolences to the country and families "who have suffered an inconceivable loss in the last few days".
He said the international community would not be "deterred" or "intimidated" by terrorists.
It comes as a US officer confirmed two Americans were also killed in the bombings
An American survivor of the Brussels airport bombing - who also survived the Boston bombing - has recounted the deadly attack.
A British woman captured in amateur footage huddling with her family after the Brussels airport blasts has spoken of her ordeal.
After escaping the Brussels Airport suicide attacks, Sneha Mehta wrote an inspirational message of hope and peace for her unborn child.