General Dynamics Ordnance & Tactical Systems and American Ordnance LLC will compete for individual orders of the rounds under the $993.7 million contract, the Army said in a statement.

The aim is to produce between 12,000 and 20,000 additional rounds per month, it added.

The announcement comes after the Army awarded $522 million in orders for the same rounds to two other companies in a deal funded by the Pentagon's Ukraine Security Assistance Initiative.

Ukraine and Russia have fired huge amounts of artillery munitions at each other since the Russian invasion began almost a year ago.

In November, a US official said Russian forces were firing about 20,000 artillery rounds a day.

Ukraine's rate was between 4,000 and 7,000 rounds per day -- faster than allied Western manufacturers can produce to keep pace.

The rates have plunged since then, as the winter set in and both sides face shortages and conserve ammunition.