WASHINGTON (Reuters) - Alliant Techsystems Inc has won a contract valued at up to $8.4 billion to supply small-caliber ammunition to the U.S. Army and continue operating the Lake City Army Ammunition Plant in Independence, Missouri, the Pentagon announced on Thursday.

The fixed-price contract runs through September 30, 2022, the Pentagon said in its daily digest of major contracts.

On Monday, ATK announced it had been selected to provide the ammunition and manage the Lake City plant, but did not provide the value of the contract.

It said the deal included an initial seven-year contract and options for three additional years.

(Reporting By Andrea Shalal-Esa; Editing by Bernard Orr and David Gregorio)