WASHINGTON (AP) — Ukrainian President Volodymyr Zelenskyy on Sunday will visit the Pennsylvania ammunition factory that is producing one of the most critically needed munitions for his country’s fight to fend off Russian ground forces.

He is expected to go to the Scranton Army Ammunition Plant to kick off a busy week in the United States shoring up support for Ukraine in the war, according to two U.S. officials and a third familiar with Zelenskyy’s schedule who spoke on the condition of anonymity to provide details that were not yet public. He also will address the U.N. General Assembly annual gathering in New York and travel to Washington for talks on Thursday with President Joe Biden and Vice President Kamala Harris.

The Scranton plant is one of the few facilities in the country to manufacture 155 mm artillery shells. They are used in howitzer systems, which are towed large guns with long barrels that can fire at various angles. Howitzers can strike targets up to 15 miles to 20 miles (24 kilometers to 32 kilometers) away and are highly valued by ground forces to take out enemy targets from a protected distance.

Ukraine has already received more than 3 million of the 155 mm shells from the U.S.

With the war now well into its third year, Zelenskyy has been pushing the U.S. for permission to use longer range missile systems to fire deeper inside of Russia.

So far he has not persuaded the Pentagon or White House to loosen those restrictions. The Defense Department has emphasized that Ukraine can already hit Moscow with Ukrainian-produced drones, and there is hesitation on the strategic implications of a U.S.-made missile potentially striking the Russian capital.

Russian President Vladimir Putin has warned that Russia would be “at war” with the United States and its NATO allies if they allow Ukraine to use the long-range weapons.

At one point in the war, Ukraine was firing between 6,000 and 8,000 of the 155 mm shells per day. That rate started to deplete U.S. stockpiles and drew concern that the level on hand was not enough to sustain U.S. military needs if another major conventional war broke out, such as in a potential conflict over Taiwan.

In response the U.S. has invested in restarting production lines and is now manufacturing more than 40,000 155 mm rounds a month, with plans to hit 100,000 rounds a month. During his visit, Zelenskyy is expected meet and thank workers who have increased production of the 155 mm rounds over the past year.

Two of the Pentagon leaders who have pushed that increased production through — Doug Bush, assistant secretary of the Army for acquisition, logistics and technology and Bill LaPlante, the Pentagon’s top weapons buyer — are also expected to join Zelenskyy at the plant, as is Gov. Josh Shapiro, D-Pa.

The 155 mm rounds are just one of the scores of ammunition, missile, air defense and advanced weapons systems the U.S. has provided Ukraine — everything from small arms bullets to advanced F-16 fighter jets. The U.S. has been the largest donor to Ukraine, providing more than $56 billion of the more than $106 billion NATO and partner countries have collected to aid in its defense.

Even though Ukraine is not a member of NATO, commitment to its defense is seen by many of the European nations as a must to keep Putin from further military aggression that could threaten bordering NATO-member countries and result in a much larger conflict.

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Associated Press writer Aamer Madhani contributed to this report.