President Joe Biden on Thursday announced an additional $800 million package in military assistance to Ukraine -- as well as a ban on all Russian-affiliated ships from U.S. ports -- as Russian forces launch a long-expected, large-scale campaign to seize the country's east.
"We're in a critical window now of time where -- they're going to set the stage for the next phase of this war," Biden said from the White House Roosevelt Room, adding the U.S. and allies will continue to provide Ukraine with "equipment they need -- their forces need -- to defend their nation."
Biden said the new aid package will include "heavy artillery weapons, dozens of howitzers, and 144,000 rounds of ammunition to go with those howitzers," as well as tactical drones.
It follows another of similar size, which Biden announced last week, but focuses more on artillery and ammunition, U.S. officials told ABC News earlier this week.
"Every American taxpayer, every member of our armed forces can be proud of the fact that our country's generosity -- and the skill and service of our military -- helped arm and repel Russia's aggression in Ukraine to beat back Putin's savagery that tried to seize Ukraine's capital and wipe out Ukraine's government," Biden said from the White House.
MORE: Biden announces $800M in new military aid for Ukraine
With this latest package, the U.S. is on track to having announced about $3 billion in military aid since the start started in late February. In particular, this is the eighth tranche of U.S. assistance from the Pentagon's existing stockpile, using what's known as presidential drawdown authority to expedite delivery.
Evan Vucci/AP
President Joe Biden delivers remarks on the Russian invasion of Ukraine, in the Roosevelt Room of the White House, April 21, 2022, in Washington, D.C.
Biden also announced Thursday that the United States will ban Russian-affiliated ships from the U.S.
"That means no ship, no ship that sails on the Russian flag or that is owned or operated by Russian interest would be allowed to dock on the united States port or access our shores. None," he said.
After meeting with Ukraine's Prime Minister Denys Shmyhal ahead of his remarks, Biden again called on Congress to provide more funding for weapons and ammunition because existing money is "almost exhausted," he said.
MORE: Biden administration fast-tracking Ukrainian refugees into US
Russia offered another ultimatum Wednesday to allow Ukrainian fighters to leave a steel plant in Mariupol -- but those fighters, for days, have refused to surrender. Finally seizing the strategic port city after weeks of besiegement and bombardment would help give Russian forces a land bridge between Crimea, which Russia has occupied since 2014, and the eastern provinces known as the Donbas, where Russian-led separatists have battled the Ukrainian government since 2014, too.
The Donbas is expected to be Russia's focus now, but the U.S. remains concerned that Russian forces will target the paths in western Ukraine being used to ship Western military aid into the country, a defense official told ABC News.
While they have not done so yet, cutting off those supply routes will help the Kremlin isolate Ukrainian forces in the east, the official added.
MORE: Tens of thousands feared dead in Mariupol as Russia renews assault in eastern Ukraine
Gleb Garanich/Reuters
Ukrainian service members hold their weapons, amid Russia's invasion of Ukraine, near the village of Kozarovychi , in Kyiv region, Ukraine April 2, 2022.
The U.S. believes Russians will target the paths in western Ukraine being used to ship in Western military aid in order to isolate Ukrainian forces in the east, a defense official told ABC News.
"Right now, we know from our discussions with the Ukrainians that they are getting this material," a defense official said Tuesday. "It's getting into the hands of their fighters."
MORE: Russian offensive 'limited' so far, fall of Mariupol 'not inevitable': Pentagon update Day 55
The U.S. and other Western countries have now provided Ukraine with close to 70,000 anti-tank weapons, including several varieties of shoulder-fired missiles. The number of shoulder-fired anti-aircraft missiles that the U.S. and other countries have sent to Ukraine is nearing 30,000.
Those missiles have been used by Ukrainian forces to great effect, but as the battle shifts from Ukraine's major cities and suburbs to the more flat eastern provinces, Kyiv's troops will need more artillery and ammunition instead.
Pavel Klimov/Reuters
An aerial view shows a residential building destroyed during Ukraine-Russia conflict in the southern port city of Mariupol, Ukraine, April 18, 2022.
Four flights carrying military aid from the $800 million drawdown package Biden announced last week arrived in Ukraine over the last 24 hours, some of them carrying U.S. howitzers and 155mm ammunition for them, a senior defense official said Wednesday, adding more equipment will arrive over the next 24 hours.
MORE: If Russia takes Mariupol, forces could be freed to fight in east: Pentagon update Day 54
ABC News asked the official why the U.S. decided to send U.S. artillery to the Ukrainians.
"We're mindful of the importance of artillery in the fight that they're in right now and in the fighting in the days to come because of the terrain, and because of what we think they're going to be up against with Russian forces," the official responded. Another reason was "the fact that it wouldn't require an onerous amount of training for the Ukrainians to know how to use them" and the ability to ship them quickly, according to the official.
Alexander Ermochenko/Reuters
A woman with a child talks to service members of pro-Russian troops as evacuees board buses to leave the city during Ukraine-Russia conflict in the southern port of Mariupol, Ukraine, April 20, 2022.
More than 5 million people have fled Ukraine since the start of the war, according to the United Nations.
MORE: Russia-Ukraine live updates: Russian forces try to storm steel plant in Mariupol
After Biden called Russia's actions in Ukraine "genocide" for the first time last week, Secretary of State Antony Blinken warned Wednesday that the same horrors witnessed in Bucha -- "death, destruction, atrocities" -- may take place in the eastern city of Mariupol "at some point," even as Russian forces seem already poised to fully capture the strategic city.
"We can only anticipate that when this tide also at some point recedes from Mariupol, we're going to see far worse -- if that's possible to imagine," Blinken said. "So the conditions there, the situation there as a result of this Russian aggression are truly horrific."