The UK's departure from the European Union will have no impact on security and defense in Europe," Williamson said in a speech to the Atlantic Council in Washington before meeting his US counterpart Jim Matisse. 

"Britain is a great world player, we have always been a first class military force, and we will always be a first class military force," he said.

"In a way, the EU has narrowed our vision and discouraged us from looking to the horizon. Now that we are free to go further and achieve higher goals, the UK is determined to seize these new opportunities," he added. 

The remarks came at a time when British Prime Minister, Teresa May, appeared to have declined in June to comment on the future status of the British military. 

Williamson's visit is aimed at convincing Americans that the UK will remain a reliable ally.