July 1 (Reuters) - NATO is set to announce at next week's Ankara summit that its European members have filled almost all the gaps left by the United States in the alliance's defence plans, a NATO source told Reuters on Wednesday.

The main gap NATO is still struggling to plug is in strategic bombers, where the U.S. has said it will make only one aircraft available instead of two, said the source, speaking on condition of anonymity.

(Reporting by Sabine Siebold, editing by Bart Meijer)