WASHINGTON

US President Joe Biden signed off on Friday on a $270 million military aid package for Ukraine as his Defense Department mulls the possibility of providing Kyiv with US fighter jets.

National Security Council spokesman John Kirby tamped down expectations on the Pentagon reaching a decision on the planes anytime soon, stressing that discussions are currently in their "preliminary" phase.

"It's not going to be something that they're going to be able to execute immediately, or even in the short term, because integrating and operating any kind of aircraft, especially advanced fighter aircraft, with complex sensors and systems, and weapons capabilities, that's a that's a difficult endeavor," he told reporters.

"There's some exploratory thinking, and you've got to think about things like training, sustainment, maintenance, that these aircraft will be requiring," said Kirby, emphasizing that the Pentagon is mulling the provision of US aircraft, not former Soviet jets.

The comments come as Biden signs off on some $270 million in new military aid for Ukraine to sustain its effort to combat Russia's efforts to forcibly seize wide swathes of the eastern European country.

The package includes roughly $100 million for 580 new Phoenix Ghost drones, a suicide drone internally-developed by the Air Force, and about $170 million in what is known as a presidential drawdown, which is the transfer of existing equipment from US stocks.

That includes four new long-range High Mobility Artillery Rocket Systems (HIMARS), which Ukraine's military has been using to strike Russian supply networks and command and control centers in eastern and southern Ukraine. Some 36,000 artillery rounds are also being sent to Ukraine to arm previously-supplied Howitzer systems, and the US is sending additional anti-armor systems.

The US has now provided Ukraine with more than $8.2 billion in assistance since Biden assumed office, according to the White House.