John Kirby, spokesperson for the US Department of Defence, said the transfer of jets "may be mistaken as escalatory and could result in a significant Russian reaction".
This was Wednesday's live blog. For the latest updates on Thursday click here.
The United States said on Wednesday it would oppose any plan for NATO nations to provide fighter jets to Ukraine, saying it would be seen as "escalatory" by Russia.
John Kirby, spokesperson for the US Department of Defence, told reporters that Secretary Lloyd Austin had stressed to his Polish counterpart and that the US "do not support the transfer of additional fighter aircraft to the Ukrainian Air Force at this time, and therefore had no desire to see them in our custody either."
"The intelligence community has assessed the transfer of MiG-29s to Ukraine may be mistaken as escalatory and could result in a significant Russian reaction that might increase the prospects of a military escalation with NATO. Therefore, we also assess the transfer of the MiG 29 to Ukraine o be high risk," he said.
He added that they believe there are "alternative options that are much better suited to support the Ukrainian military in their fight against Russia."
His comments came after Russian troops carried out a "direct strike" on a maternity hospital in the besieged city of Mariupol, Ukrainian President Volodymyr Zelenskyy said.
He said that people and children were under the rubble, calling the strike an "atrocity" as the Russian invasion continues.
A planned evacuation of the city — the third one — failed once more.
Here a recap of how Wednesday unfolded: