For Ukraine's defense against Russian drone and cruise missile attacks, the US is thinking about sending older HAWK air defense equipment from storage, according to two US officials who spoke to Reuters.

The HAWK interceptor missiles would be an improvement over the Stinger missile systems, a smaller, shorter range air defense system that the US already sent to thwart the Russian invasion.

Using the Presidential Drawdown Authority (PDA), the Biden administration would transfer the HAWK equipment, which is based on technology from the Vietnam War era but has undergone numerous upgrades. In response to an emergency, the PDA enables the United States to swiftly transfer defense goods and services from stocks without congressional approval.

How many HAWK systems and missiles the US has available for transfer is unknown to Reuters. The White House chose not to respond.

According to U.S. officials speaking to Reuters, the HAWK system is the forerunner of Raytheon Technologies' (RTX.N) PATRIOT missile defense system, which is not an option for Ukraine.

Following a devastating Russian missile barrage earlier this month, U.S. President Joe Biden promised Ukraine President Volodomyr Zelenskiy that Washington would give Ukraine advanced air systems. View More

According to Jens Stoltenberg, the secretary general of NATO, Spain plans to send four HAWK launchers. View More

Because it was uncertain whether enough American launchers were in good condition, the United States would probably initially send interceptor missiles for the HAWK system to Ukraine, a U.S. official told Reuters. The American systems have been stored for many years.

U.S. officials have stated that a PDA is being considered for later this week. It would probably be half as big as the most recent security assistance packages, which have been around $700 million in size, according to a U.S. official.

Although it was not immediately clear whether HAWK interceptor missiles would be included, American officials have previously issued a warning that the size and makeup of military aid packages can quickly change.

The Russian invasion of neighboring Ukraine on February 24 has been referred to as a "special military operation" by Moscow. Since then, the US has provided Kyiv with security assistance worth about $17.6 billion.