Defence secretary Michael Fallon has received reassurances from his US counterpart that security ties with Britain will "endure" in light of the vote to leave the European Union.
In return, Fallon told Ash Carter that the UK would remain committed to tackling global security issues and continue in the fight against Islamic State as a member of Nato.
The pair spoke by phone on Friday after it was announced Britain had voted to sever ties with Brussels.
"The secretary reaffirmed that those bonds endure after yesterday's vote by the United Kingdom to exit the European Union," Pentagon spokesman Peter Cook said.
Carter emphasised the UK's role as a "vital" member of Nato and welcomed Fallon's assurances that Britain will continue to play an active role in global security issues.