WASHINGTON -- The Pentagon will announce it is sending up to US$500 million in military aid to Ukraine, including more than 50 heavily armored vehicles and an infusion of missiles for air defense systems, U.S. officials said Monday, as Ukrainian and Western leaders try to sort out the impact of the brief weekend insurrection in Russia.

The aid is aimed at bolstering Ukraine's counteroffensive, which has been moving slowly in its early stages. It wasn't clear Monday if Ukrainian forces will be able to take advantage of the disarray in the Russian ranks, in the aftermath of the short-lived rebellion by Yevgeny Prigozhin and the Wagner mercenary group that he has controlled.

An announcement on the aid package is expected Tuesday. This would be the 41st time since the Russian invasion into Ukraine in February 2022 that the U.S. has provided military weapons and equipment through presidential drawdown authority. The program allows the Pentagon to quickly take items from its own stocks and deliver them to Ukraine.

Because the aid packages are generally planned in advance and recently included many of the same critical weapons for the battlefront, the contents weren't likely chosen based on the weekend rebellion.

But, the missiles and heavy vehicles can be used as Ukraine tries to capitalize on what has been a growing feud between the Wagner Group leader and Russia's military brass, with simmering questions about how many of Prigozhin's forces may leave the fight.

The mercenaries left Ukraine to seize a military headquarters in a southern Russian city and moved hundreds of miles toward Moscow before turning around after less than 24 hours on Saturday.

According to the officials, the U.S. will send 30 Bradley Fighting Vehicles and 25 of the armored Stryker vehicles to Ukraine, along with missiles for the High-Mobility Artillery Rocket System (HIMARS) and the Patriot air defense systems. The package will include Javelin and high-speed anti-radiation (HARM) missiles, demolition munitions, obstacle-clearing equipment and a wide range of artillery rounds and other ammunition.

The officials spoke on condition of anonymity because the aid has not yet been publicly announced.

According to the Pentagon, the U.S. has delivered more than US$15 billion in weapons and equipment from its stocks to Ukraine since the Russian invasion, and has committed an additional US$6.2 billion in supplies that haven't yet been identified. The more than US$6 billion extra is the result of an accounting error, because the military services overestimated the value of the weapons they pulled off the shelves and sent to Ukraine over the past year.

More broadly, the U.S. has also promised to send more than US$16.7 billion in longer-term funding for various weapons, training and other equipment through the Ukraine Security Assistance Initiative, and an additional roughly US$2 billion in foreign military financing.

The U.S. has at least US$1.2 billion in drawdown authority that hasn't yet been committed but will expire at the end of this fiscal year on Sept. 30. The remaining US$1.9 billion in USAI funds does not expire until the end of the next fiscal year, in September 2024.

------

Associated Press writer Aamer Madhani contributed to this report.