Britain will buy an additional C-17 military transport aircraft from U.S. firm Boeing, Prime Minister David Cameron said on Wednesday.

I can announce today .... we will be able to purchase an additional C-17 for the RAF (air force), he told parliament.

Britain currently has seven C-17s. The defence ministry was not immediately able to disclose the cost of the purchase.

(Reporting by Mohammed Abbas, editing by Matt Falloon)