(CNN) — The Pentagon said on Wednesday that the United States earlier this month delivered long-range missiles to Ukraine that Joe Biden's administration had previously refused to send following an order from the US president.

Biden secretly approved the transfer of ATACMS long-range missiles inside Ukrainian territory in February. The ATACMS missiles were quietly included in a $300 million aid package announced March 12 and finally delivered to Ukraine earlier this month, Pentagon spokesman Lt. Col. Caron Corn said.

“It was not announced at the time that we were providing Ukraine with this new capability to maintain Ukraine's operational security at Ukraine's request,” Corn said, referring to questions about its use for the Ukrainian military.

The Biden administration has opposed the deployment of long-range missiles, partly for preparedness reasons. Manufacturing these powerful missiles requires time and complex components. Lockheed Martin, which makes the ATACMS missiles, is in full production and produces about 500 missiles a year, a company spokesman said in September.

And the U.S. worked behind the scenes to address readiness issues, including procuring ATACMS missiles and replenishing U.S. military reserves.

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

A US official said Biden instructed his team to take the action following Russia's acquisition and use of North Korean missiles against Ukraine and Russian attacks on civilian infrastructure in Ukraine.

“We warn Russia against acquiring North Korean ballistic missiles and against renewing attacks on Ukraine's civilian infrastructure,” Dietz said. “Our readiness concerns were addressed and we were able to follow through on our warning and deliver this long-range capability to Ukraine.”

More missiles are expected to be included in a new military aid package announced by the Pentagon this Wednesday Biden will compose A nearly $61 billion aid package for Ukraine after months of delays in Congress.

Last fall, the United States sent to Ukraine for the first time the medium-range variant of the ATACMS missile system, which can reach about 160 kilometers, while the long-range version can reach up to 305 kilometers.

Ukrainian officials have privately and publicly asked the United States to launch long-range missiles deep behind Russian borders. U.S. officials previously resisted, citing supply problems and concerns about further provoking Moscow if they were sent.