The orders, officially decided on January 30, went to Northrop Grumman Systems Corp. and Global Military Products Inc. and came amid worries that Ukraine was fast depleting the stockpiles of artillery shells from the United States and other allies.

Deliveries of the new ammunition are scheduled to begin in March of this year, the Army said in a statement.

The contract is 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.

"The war in Ukraine is consuming an enormous amount of munitions, and depleting allied stockpiles," NATO chief Jens Stoltenberg said Monday.

"The current rate of Ukraine's ammunition expenditure is many times higher than our current rate of production. This puts our defense industries under strain," he said.