United States Vice President Kamala Harris says her country and Poland will work together to support the humanitarian and security needs of Ukraine.

Harris met Polish President Andrzej Duda and spoke at a joint news conference in Poland's capital of Warsaw on Thursday.

Harris announced the US had delivered two Patriot missile defense systems to Poland. She said, "The United States is prepared to defend every inch of NATO territory."

The US had earlier rejected Poland's offer to send its MiG-29 fighter planes to a US base in Germany for transfer to Ukraine in exchange for the provision of alternative jets for its own use.

The US said providing fighter jets to Ukraine in such a way could increase the prospects of military tensions between Russia and NATO.

Duda said regarding the offer, "We wanted NATO as a whole to make a common decision."

Duda also said he asked Harris to accelerate the delivery of F-35 fighter planes and tanks to boost Poland's defensive capabilities.