The U.S. will send another $400 million in military equipment to Ukraine, including four more advanced rocket systems, a senior defense official said Friday, in an effort to bolster Ukrainian efforts to strike deeper behind Russian frontlines in the eastern Donbas region.

The aid comes as Moscow this week claimed full control of Ukraine’s Luhansk province in the Donbas, but Ukrainian officials say their troops still control a small part of the province and fierce fighting continues in several villages.

The defense official said that the eight High Mobility Artillery Rocket Systems, or HIMARS, that were previously sent are still being used by Ukraine forces in the fight. And this will give them four more to help hit Russian command and control nodes, logistics capabilities and other systems that are further back behind the battlefront. The official spoke on condition of anonymity to discuss details not yet made public.

Russia in recent days has launched dozens of missiles across Ukraine and pinned down Ukrainian forces with continuous long-range fire for sometimes hours at a time. Ukraine’s leaders have publicly called on Western allies to quickly send more ammunition and advanced systems that will help them narrow the gap in equipment and manpower. The precision weapons can help Ukraine hit Russian weapons that are farther away and are being used to bombard Ukrainian locations.

The latest aid is the 15th package of military weapons and equipment transferred to Ukraine from Defense Department stocks since last August. In addition to the HIMARS, the U.S. will also send 1,000 rounds of 155 millimeter artillery which has an increased precision capability that also will help Ukraine hit specific targets. The package also will include three tactical vehicles, counter battery radar systems, spare parts and other equipment.

Looking ahead to the coming months, the official said that a key goal is to build up Ukraine’s logistics and repair capabilities so troops can maintain its weapons systems and continue the fight into the future.

Overall, the U.S. has sent about $7.3 billion in aid to Ukraine since the war began in late February.

Luhansk is one of two provinces that make up the Donbas, a region of mines and factories where pro-Moscow separatists have fought Ukraine’s army for eight years and declared independent republics that Russian President Vladimir Putin recognized before he sent troops into Ukraine.

Putin on Thursday warned that Kyiv should accept Moscow’s terms or brace for the worst, saying that Russia hasn’t yet “started anything in earnest.”

U.S. and other western officials have said that Russia has been making slow, incremental progress in the Donbas but has not made gains as rapidly as Moscow initially intended. President Joe Biden has said that the U.S. is giving Ukrainians the aid needed to continue to resist Russian aggression.

“I don’t know how it’s going to end, but it will not end with a Russian defeat of Ukraine in Ukraine,” Biden said last week.

(AP)