The United States is finalizing plans to send the Patriot missile defense system to Ukraine, a decision that could be announced as soon as this week, three U.S. officials told Reuters on Tuesday.

Ukraine has asked its Western partners for air defenses, including U.S.-made Patriot systems, to protect it from Russian missile bombardment.

Ground-based air defense systems, such as Raytheon Technology Corp's Patriot, are built to intercept incoming missiles.

The Patriot is considered to be one of the most advanced U.S. air defense systems and is usually in short supply, with allies around the world vying for it.

"It's very, very significant," said Alexander Vindman, a retired army lieutenant colonel who led Ukraine policy at the White House during the administration of President Donald Trump.

The Patriot system is usually used against more advanced threats including aircraft, cruise missiles and ballistic missiles and typically includes launchers along with radar and other support vehicles.

Two of the officials, speaking on condition of anonymity, said the announcement could come as early as Thursday but was awaiting formal approval from U.S. Defense Secretary Lloyd Austin and President Joe Biden.

The Pentagon declined comment on reports about the Patriot system at a news briefing.

There was no immediate comment from Ukrainian officials, but Kyiv held high-level military talks on Tuesday with Washington, Ukraine President Volodymyr Zelenskyy's office said.

One of the officials said Ukrainian forces would likely be trained in Germany before the Patriot equipment was sent to Ukraine. Vindman said the training could take several months.

Details such as the version of the Patriot missile defense system, its range or how many units would be sent were not immediately available.

It was unclear if the United States would limit how the Ukrainians employ the Patriot system. Washington has restricted use of High Mobility Artillery Rocket System (HIMARS) launchers to targets inside Ukraine.

Former Russian President Dmitry Medvedev has warned NATO against providing Ukraine with Patriot missile defenses, and it is likely Moscow will view the move as an escalation.

The United States has provided Ukraine with $19.3 billion in military assistance since Russia launched its "special military operation" on February 24.

(Cover: A combat-ready Patriot anti-aircraft missile system of the Bundeswehr's anti-aircraft missile squadron 1 stands on the airfield of Schwesing military airport, Schleswig-Holstein, Schwesing, Germany, March 17, 2022. /CFP)

(With input from Reuters)