Top US General Mark Milley has defended himself after a book reported he had "secret" phone calls with China amid concerns about then-President Donald Trump.

The calls last October and January were to reassure the Chinese military, Gen Milley said on Wednesday.

Mr Trump said the claims were fabricated and Republicans have called for the general to be fired.

President Joe Biden said he has "great confidence" in Gen Milley.

Gen Milley's spokesman said that the calls were in keeping with his "duties and responsibilities conveying reassurance in order to maintain strategic stability".

The phone calls to Chinese General Li Zuocheng were revealed on Tuesday in extracts from a new book by Washington Post investigative reporters. They were made just after the presidential election and after Mr Trump refused to accept his defeat.

The book, "Peril", said that after the January 6 riots, Gen Milley, Chairman of the Joint Chiefs of Staff, "was certain that Trump had gone into a serious mental decline in the aftermath of the election".