WASHINGTON (AP) — The U.S. is expected to announce a new $400 million package of military aid for Ukraine on Friday, U.S. officials said, as Kyiv struggles to hold off advances by Russian troops in the northeast Kharkiv region.

This is the third tranche of aid for Ukraine since Congress passed supplemental funding in late April after months of gridlock. Ukrainian President Volodymyr Zelenskyy had warned Thursday that his country was facing "a really difficult situation" in the east, but said a new supply of U.S. weapons was coming and "we will be able to stop them."

According to officials, the package includes artillery, air defense and anti-tank munitions, armored vehicles and other weapons and equipment. The officials spoke on condition of anonymity because the aid has not yet been announced. It will be provided through presidential drawdown authority, which pulls systems and munitions from existing U.S. stockpiles so they can be sent quickly to the war front.

Almost immediately after President Joe Biden signed the $95 billion foreign aid package, the Pentagon announced it was sending $1 billion in weapons through that drawdown authority,. And just days later the Biden administration announced a $6 billion package funded through the Ukraine Security Assistance Initiative, which pays for longer-term contracts with the defense industry and means that the weapons could take many months or years to arrive.

Russia has sought to exploit Ukraine's shortages of ammunition and manpower as the flow of Western supplies since the outbreak of the war petered out while Congress struggled to pass the bill. Moscow has assembled large troop concentrations in the east as well as in the north and has been gaining an edge on the battlefield, Zelenskyy said.