Germany, where the decision to send Leopard tanks was seen as a major strategic turnaround, has ruled out sending warplanes.
Poland said on Tuesday it was not having official discussions on transferring any of its F-16 s to Ukraine.
Britain hasn't ruled out sending its combat planes.
The prime minister's official spokesman said that the UK's F-35 fighter jets and Typhoon are extremely sophisticated and take months to learn how to fly.
We don't believe it is practical to send those jets into Ukraine. France's President Emmanuel Macron said that his country had not ruled out the delivery of fighter planes, but that Ukraine had not yet made such a request.
Others could be more eager to help.
Slovakia has said it will be prepared to send over MiG 29 fighter jets, while Dutch politicians recently floated the idea of sending Ukraine the F 16 jets it wants.
Olivier Fourt, a journalist specialised in military aircraft, said it was no surprise that Kyiv had its heart set on that model.
He said that the F-16 is one of the most produced fighter aircraft in the world, and there are many of them. Many European countries have some, he said. It is an excellent fighter jet, but in the United States the re-exportation rules are very strict. Experts believe that bolstering the Ukrainian air force could allow Kyiv to attack Russian troops deep in occupied territory and dissuade Russian bombers from hitting civilian and energy infrastructure in land it still controls.
They warned that the warplanes would not be a miracle solution to defeat the Russians.
Justin Bronk, a researcher at the UK-based RUSI think tank, said Western fighters will give a major boost to Ukrainian air force survivability and air-to-air lethality against Russians.
He wrote on Twitter that they would still be at risk from Russia's surface-to-air missile systems and have limited ground attack options.
In order to be trained up to fly the new planes, Ukrainian pilots will need to be found, said retired NATO general Jean-Paul Palomeros.
How many are still operational today? He asked.
The specialist Oryx site, which tracks destroyed aircraft, says Ukraine lost more than 50 Soviet-era combat planes in less than a year since Russia invaded.
He said that you can't draw up an air force overnight.
He suggested that long-range missiles might be as useful as they are, but easier to supply.