WASHINGTON, May 31 - The Biden administration plans to sell Ukraine four MQ-1C Gray Eagle drones that can be armed with Hellfire missiles for battlefield use against Russia, Reuters reported citing three people familiar with the situation.

The sale of the General Atomics-made drones could still be blocked by Congress, the sources said, adding that there is also a risk of a last minute policy reversal that could scuttle the plan, which has been under review at the Pentagon for several weeks.

Ukraine has been using several types of smaller shorter range unmanned aerial systems against Russian forces that invaded the country in late February. They include the AeroVironment RQ-20 Puma AE, and the Turkish Bayraktar-TB2.

But the Gray Eagle represents a leap in technology because it can fly up to 30 or more hours depending on its mission and can gather huge amounts of data for intelligence purposes. Gray Eagles, the Army's version of the more widely known Predator drone, can also carry up to eight powerful Hellfire missiles.

The sale is significant because it puts an advanced reusable U.S. system capable of multiple deep strikes on the battlefield against Russia for the first time.

The administration of President Joe Biden intends to notify Congress of the potential sale to Ukraine in the coming days with a public announcement expected after that, a U.S. official said.

A White House spokesperson referred inquiries to the Pentagon and a Pentagon spokesperson said there was "nothing to announce."

Money from the recently passed $40 billion Ukraine Security Assistance Initiative has been set aside to fund both the possible sale and the training needed for the drones, the U.S. official and one of the people familiar said.

The MQ-1C is also compatible with a greater variety of munitions than the Bayraktar-TB2. The Ukrainian Bayraktars are equipped with 22 kg (48 pound) Turkish-made MAM-L missiles, around half the weight of a Hellfire.

Training on the UAV system made by General Atomics usually takes months, Gettinger said, but a notional plan to train experienced Ukrainian maintainers and operators in a handful of weeks has been proposed in recent weeks, the sources said. (rt/ez)