PARIS, Feb 1 (AFP) - Western countries have only just approved sending battle tanks to Ukraine, but Kyiv is already requesting F-16 warplanes to help repel the Russian invasion.

While the United States has for now ruled that out, a few European nations appear more open to the idea.

US President Joe Biden on Monday (Jan 30) appeared to draw the line on supplying American fighter jets to Kyiv.

"No," he said when asked by reporters at the White House if he was in favour, though the next day he said he would talk to his Ukrainian counterpart Volodymyr Zelenskyy about his latest requests for advanced weaponry.

In the early months of Russia's invasion of Ukraine, Kyiv's partners were reluctant to provide too much military aid, eager to avoid a more direct confrontation between the West and Russia.

But as the war grinds on, they have repeatedly given in to Ukraine's appeals for more substantial weapons.

In December, Washington finally agreed to send its high-performing Patriot air defence missiles. In January, it announced it would also be sending Abrams battle tanks.

After pressure from allies, Germany in January approved sending Leopard tanks to Kyiv - and said it would agree to requests from other European countries who wanted to send their own German-made Leopards.

Ukrainian Defence Minister Oleksiy Reznikov said on Tuesday during a visit to France that his country was used to having its pleas for more equipment denied at first.

"For each initial request, we first have to fight against this 'no'. (But) it means 'no today'," he said.

"Let me remind you that, with the German Leopard tank, it was 'no' at first. But now we have a coalition of tanks."

Olivier Schmitt, a researcher at the Denmark-based Center for War Studies, said he did not think sending planes would escalate the conflict.

"Delivering fighter jets like the F-16s, which would allow Kyiv to wage an even more effective air-ground campaign, would not signal a symbolic breaking point or constitute an escalation," he wrote in the geopolitics journal Le Grand Continent.

"This type of air-ground combat is typical of modern warfare".

But European capitals are undecided.

Germany, where the decision to send the Leopard tanks was seen as a major strategic turnaround, has ruled out sending warplanes.

Poland on Tuesday said it was not having "official discussions" on transferring any of its F-16s to Ukraine.

Britain appeared to rule out sending its combat planes.

"The UK's Typhoon and F-35 fighter jets are extremely sophisticated and take months to learn how to fly," the prime minister's official spokesman said.

"We believe it is not practical to send those jets into Ukraine."

France's President Emmanuel Macron said 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 would 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 Kyiv had its heart set on that model.

"The F-16 is one the most produced fighter aircraft in the world, so there are lots of them, many European countries have some," he said. And "it's an excellent fighter jet".

But "in principle, in the United States, re-exportation rules are very strict."