Visiting Brussels, U.S. Secretary of State John Kerry expressed solidarity with Belgium on March 25 after suicide bombings killed 31 people in the country's capital.
Standing alongside Belgian Prime Minister Charles Michel, Kerry dismissed criticism of Belgium's failure to prevent the March 22 attacks claimed by the Islamic State (IS) group, saying the Belgian government had acted forcefully to fight terrorism.
Kerry also said the IS group would be destroyed.
"We will not be intimidated,” he said. “We will not be deterred."
Michel has refused to accept the resignations of his interior and justice ministers after they offered to take responsibility for failing to prevent the attacks.
Belgian police have arrested six people in Brussels as part of the investigation into the bombings, which have been linked to the November Paris attacks in which 130 people died.