(CNN) — The US delivered long-range missiles to Ukraine earlier this month that the Biden administration had previously refused to send following a directive from President Joe Biden, the Pentagon said Wednesday.

Biden secretly approved the transfer of the long-range ATACMS missiles in February for use inside Ukrainian territory. The ATACMS missiles were then quietly included in the $300 million aid package announced on March 12 and ultimately delivered to Ukraine earlier this month, according to Pentagon spokesman Lt. Col. Garron Garn.

“It was not announced that we are providing Ukraine with this new capability at the time in order to maintain operational security for Ukraine at their request,” Garn said, deferring questions about their use to Ukraine’s military.

The Biden administration had resisted sending the long-range missiles in part because of readiness concerns. The powerful missiles require time and complex components to produce. Lockheed Martin, which manufactures the ATACMS missiles, is in full-rate production and produces approximately 500 missiles per year, a spokesman for the company said in September.

The US worked behind the scenes to address the readiness concerns, which included buying more ATACMS missiles and filling US military stocks.

“As a result, we were able to move forward with this provision of ATACMS while also maintaining the current readiness of our armed forces,” said Pentagon spokesman Maj. Charlie Dietz.

Biden also directed his team to take this step following Russia’s procurement and use of North Korean ballistic missiles against Ukraine, and Russia’s attacks on civilian infrastructure in Ukraine, a US official said.

“We had warned Russia against acquiring North Korean ballistic missiles and against renewing its attacks against Ukraine’s civilian infrastructure,” Dietz said. “With our readiness concerns resolved, we were able to follow through on our warning and provide this long-range capability to Ukraine.”

More of the missiles are expecting to be included in the new military assistance package the Pentagon announced on Wednesday after Biden signed into law an aid package providing nearly $61 billion in assistance for Ukraine following months of delays in Congress.

Last fall, the US first sent Ukraine the mid-range variant of the ATACMS missile system, which can reach about 100 miles, while the longer-range version can reach as far as 190 miles.

Ukrainian officials have been asking the US in private and in public for the long-range missiles to target deeper behind Russian lines. American officials have previously resisted, citing supply issues and concerns about further provoking Moscow if they are deployed.

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