President Joe Biden in a statement Wednesday said he was "proud to announce our biggest tranche of security assistance to date" to Ukraine: "approximately $2.98 billion of weapons and equipment."

"This will allow Ukraine to acquire air defense systems, artillery systems and munitions, counter-unmanned aerial systems, and radars to ensure it can continue to defend itself over the long term," Biden said.

Biden confirmed the money would come through the Ukraine Security Assistance Initiative. The USAI money can be spent on contracts with the defense industry to produce new equipment for Ukraine.

Biden in his statement also marked Ukrainian Independence Day, saying, "Ukrainians have inspired the world with their extraordinary courage and dedication to freedom."

"Today is not only a celebration of the past but a resounding affirmation that Ukraine proudly remains -- and will remain -- a sovereign and independent nation," he said.

He continued, "I know this Independence Day is bittersweet for many Ukrainians as thousands have been killed or wounded, millions have been displaced from their homes, and so many others have fallen victim to Russian atrocities and attacks."

"Today and every day, we stand with the Ukrainian people to proclaim that the darkness that drives autocracy is no match for the flame of liberty that lights the souls of free people everywhere," Biden said.

-ABC News' Ben Gittleson

Two Zaporizhzhya nuclear power plant employees were killed on their day off when Russian forces shelled the city of Enerhodar, officials said.

-ABC News’ Yuriy Zaliznyak and Dada Jovanovic

The U.S. will announce its largest single aid package for Ukraine on Wednesday, according to two U.S. officials. The package is expected to be valued at roughly $3 billion -- though one official told ABC News some changes could be made overnight, and $3 billion is on the higher end of the estimates.

A senior U.S. official told ABC News the package will come from Ukraine Security Assistance Initiative funds. Unlike presidential drawdown packages, which pull from existing U.S. equipment stocks, the USAI money can be spent on contracts with the defense industry to produce new equipment for Ukraine.

The U.S. has committed about $10.6 billion in military aid to Ukraine since the beginning of the Biden administration.

-ABC News' Matt Seyler and Shannon Crawford

The United States is once again urging its citizens to leave Ukraine amid concerns Russia is ramping up attacks on civilians in the war-torn country.

In a security alert posted Tuesday on its website, the U.S. Embassy in Kyiv urged Americans "to depart Ukraine now using privately available ground transportation options if it is safe to do so."

"The Department of State has information that Russia is stepping up efforts to launch strikes against Ukraine's civilian infrastructure and government facilities in the coming days," the embassy said in the alert. "Russian strikes in Ukraine pose a continued threat to civilians and civilian infrastructure."

Sources within the State Department said the heightened risk of a Russian strike on highly populated centers is most directly tied to Ukraine's Independence Day on Wednesday.

"The risks are really high," Ukrainian President Volodymyr Zelenskyy told ABC News. "We are receiving information that there may be a provocation by the Russian Federation, by the occupiers. Therefore, we do not want large gatherings on such days. The days are beautiful, but ... our neighbors are not."

Russian forces will "now almost certainly" switch focus to capturing Donetsk Oblast after claiming control of neighboring Luhansk Oblast in eastern Ukraine's disputed Donbas region, according to intelligence briefings from the U.K. Ministry of Defense.

Russian President Vladimir Putin declared victory in Luhansk on Monday, a day after Ukrainian troops withdrew from the city of Lysychansk -- their last stronghold of resistance in the province. Ukrainian troops had spent weeks trying to defend Lysychansk and to keep it from falling to Russian forces, as the neighboring city of Sievierodonetsk did a week ago. A river separates the two cities.

"Russia's focus will now almost certainly switch to capturing Donetsk Oblast, a large portion of which remain under the control of Ukrainian forces," the U.K. Ministry of Defense said in Monday's briefing. "The fight for the Donbas has been grinding and attritional and this is highly unlikely to change in the coming weeks."

Putin has made capturing the entire Donbas -- Ukraine's mostly Russian-speaking industrial heartland in the east -- a key goal in his war in neighboring Ukraine. Russia-backed separatists in Donbas have battled Ukrainian forces since 2014, when they declared independence from Kyiv after the Russian annexation of Ukraine's Crimean Peninsula. Moscow formally recognized the self-proclaimed republics in Luhansk and Donetsk oblasts just days before launching its Feb. 24 invasion.

"Russia's relatively rapid capture of Lysychansk extends its control across virtually all of the territory of Luhansk Oblast, allowing it to claim substantive progress against the policy objective it presented as the immediate purpose of the war, namely 'liberating' the Donbas," the U.K. Ministry of Defense said in Tuesday's briefing.

"Ukrainian forces have likely largely withdrawn in good order, in line with existing plans," the ministry continued. "The Ukrainian held areas of Sieverodonetsk-Lyschansk consisted of a bulge or salient which Russian could attack from three sides. There is a realistic possibility that Ukrainian forces will now be able to fall back to a more readily defendable, straightened front line."

"The battle for the Donbas has been characterised by slow rates of advance and Russia’s massed employment of artillery, levelling towns and cities in the process," the ministry added. "The fighting in Donetsk Oblast will almost certainly continue in this manner."