Western countries could provide the Ukrainian air force with jets and pilot training, the U.S. Air Force’s chief of staff said Wednesday, an idea that would significantly ramp up Western assistance to Ukraine as it fights off invading Russian troops—but military officials say no firm decisions have been made yet.

Air Force Gen. Charles Q. Brown said during an interview at the Aspen Security Forum “there’s a number of different platforms that could go to Ukraine,” including jets made by the United States, Sweden, France or the multi-country Eurofighter consortium.

Brown added any warplanes transferred to Ukraine—whose current air force mostly consists of Soviet-era jets—will probably be “something non-Russian,” because getting spare parts for Russian-made fighter jets could prove difficult.

Earlier Wednesday, Brown told Reuters U.S. officials are discussing whether to begin training Ukrainian pilots to fly Western jets, a process Ukraine claims is possible within a matter of weeks but Brown and other experts think could take months.

Gen. Mark Milley, chairman of the Joint Chiefs of Staff, said Wednesday the military hasn’t decided whether to start training Ukrainian pilots yet, but “we do examine a wide variety of options, to include pilot training.”