President Joe Biden said on Monday the United States would not provide F-16 fighter jets to Ukraine, as Kyiv expands the list of weaponry it needs.
Last week, Western countries, including the United States and Germany approved the delivery of heavy battle tanks to Ukraine.
The move is a departure from a previous position that tanks were considered a step too far in their support for Ukraine and could risk a widening backlash from Russia.
But Biden on Monday appeared to draw the line on supplying American fighter jets to Ukraine.
"No," he said when asked by reporters at the White House if he was in favour of sending F-16s or others.
Biden's comment came shortly after Ukrainian President Volodymyr Zelensky said Russia had begun exacting its revenge for Ukraine's resistance with relentless attacks in the east.
Zelensky has warned for weeks that Moscow aims to step up its assault after about two months of virtual stalemate along the front line that stretches across the south and east.
France and Poland, however, appear to be willing to entertain any such request from Ukraine, with Macron telling reporters in The Hague on Monday that "by definition, nothing is excluded" when it comes to military assistance.
In remarks carried on French television before Biden spoke in Washington, Macron stressed any such move would depend on several factors including the need to avoid escalation and assurances that the aircraft would not "touch Russian soil".
In Poland, Prime Minister Mateusz Morawiecki also did not rule out a possible supply of F-16s to neighbouring Ukraine, in response to a question from a reporter before Biden spoke.
Morawiecki said in remarks posted on his website that any such transfer would take place "in complete coordination" with Nato countries. (AFP/Reuters)