"It doesn't change our calculus with regards to F16s," National Security Council spokesman John Kirby told reporters, referring to the US-built fighter jet. Poland's move "does not affect, does not change" that.

Secretary of State Antony Blinken, speaking to reporters on a visit to Niger, alluded to the heavy costs of US fighter jets.

"I think it's a mistake to get focused on any particular weapons system at any given time," Blinken said.

He said it was important "not only making sure that the Ukrainians have the right weapons system but that they can use it."

"So depending on the system, that might require significant training" or maintenance, Blinken said.

"Different countries are doing different things in response to what they have and to what the perceived needs are."