Former U.S. Defense Secretary Robert Gates says Britain's defense spending cuts could limit its ability to be a full partner with the United States in military operations.

Britain's army will lose 20,000 soldiers by 2020 — shrinking from 102,000 to 82,000 as part of efforts to meet steep cuts to public spending ordered by Prime Minister David Cameron.

Telling BBC radio Thursday that he laments U.S. defense cuts too, Gates said the "fairly substantial" spending cuts mean Britain "won't have full spectrum capabilities" and the ability to be a "full partner" to the U.S.

Gates served as Pentagon chief under Presidents George W. Bush and Barack Obama and retired in 2011.

He is currently promoting a book, "Duty: Memoirs of a Secretary of War," which questions Obama's war leadership.