Large shipments of Western weapons continue to flow into Ukraine as Russia’s invasion enters its fourth week.

President Joe Biden announced an additional $800 million in new security aid to Ukraine on Thursday, hours after Ukrainian president Volodymyr Zelenskyy’s address to Congress. The U.S. weapons package to Ukraine will include eight hundred Stinger anti-aircraft systems, twenty million rounds of ammunition, 7,000 light weapons, 9,000 anti-armor systems, and one hundred drones.

"These are direct transfers of equipment from our Department of Defense to the Ukrainian military to help them as they fight against this invasion,” Biden said.

Biden singled out the anti-aircraft weapons in the aid package. He also said the United States is “helping Ukraine acquire additional longer-range anti-aircraft systems and the munitions for those systems.”

One possibility could be transferring long-range S-300 surface-to-air missile systems to Ukraine. 

"These S-300s and longer-range artillery forces is what will help close the sky” over Ukraine, said Gregory Meeks, chairman of the House Foreign Affairs Committee. "President Zelensky is not asking for American troops or American equipment or anything of that nature to close the skies. What he's asking for is the artillery that will do that. The S-300 may be the one that does that.”

CNN reported that Slovakia is considering giving Ukraine an S-300 system, but wants assurances that the weapon will be replaced immediately with a system of similar capabilities. Negotiations are reportedly underway to backfill Slovakia’s missile defense capabilities with a U.S.-made Patriot missile system, but the current status of those talks remains unclear. Slovakia is one of only three NATO members to possess the Soviet-era S-300, with the others being Bulgaria and Greece.

"I want to be honest with you. This could be a long and difficult battle,” Biden said. “But the American people will be steadfast in our support of the people of Ukraine, in the face of Putin's immoral, unethical attacks on civilian populations.”

British defense minister Ben Wallace said to the BBC on Wednesday that Britain is supplying Starstreak man-portable air-defense systems (MANPADS) to Ukraine. Wallace told U.K. lawmakers last week that London is considering delivering Starstreak systems to Ukraine, noting certain logistical challenges that include training.

Other forms of military aid to Kiev remain off the table for now. The Biden administration has declined proposals to transfer MiG-29 jet fighters from Poland to Ukraine, with U.S. defense officials claiming that the Ukrainian military is currently not in need of more aircraft and that they can fight more effectively with their western-supplied man-portable missiles. Leaders in Washington and other NATO countries have likewise repeatedly rejected Zelenskyy’s continued calls for a Western-imposed no-fly zone in Ukrainian airspace, describing the measure as a needlessly risky and escalatory step.

Mark Episkopos is a national security reporter for The National Interest.

Image: Reuters.