The Biden administration announced another $1 billion in new military aid for Ukraine on Monday, pledging what will be the biggest yet delivery of rockets, ammunition and other arms straight from Department of Defense stocks for Ukrainian forces.

The U.S. pledge of a massive new shipment of arms comes as analysts warned that Russia was moving troops and equipment in the direction of the southern port cities to stave off a Ukrainian counteroffensive.

The aid includes additional rockets for the High Mobility Artillery Rocket Systems, or HIMARS, as well as thousands of artillery rounds, mortar systems, Javelins and other ammunition and equipment. Military commanders and other U.S. officials say the HIMARS and artillery systems have been crucial in Ukraine’s ongoing fight to try to prevent Russia from taking more ground.

The latest announcement brings the total U.S. security assistance committed to Ukraine by the Biden administration to roughly $9 billion since Russian troops invaded in late February.

“At every stage of this conflict, we have been focused on getting the Ukrainians what they need, depending on the evolving conditions on the battlefield,” Colin Kahl, undersecretary of defense for policy, said in announcing the new weapons shipment.

Until now, the largest single security assistance package announcement was for $1 billion on June 15. But that aid included $350 million in presidential drawdown authority, and another $650 million under the Ukraine Security Assistance Initiative.

Monday’s package allows the U.S. to deliver weapons systems and other equipment more quickly since it takes them off the Defense Department shelves.

For the last four months of the war, Russia has concentrated on capturing the Donbas region of eastern Ukraine, where pro-Moscow separatists have controlled some territory as self-proclaimed republics for eight years. Russian forces have made gradual headway in the region while launching missile and rocket attacks to curtail the movements of Ukrainian fighters elsewhere.

(AP)