A Pakistan Air Force’s fighter jet F-16 flies during a training programme. Picture used for illustrative purposes only.

Denmark's decision to supply Ukraine with American F-16 fighter jets to fend off Russia's invasion represents an "escalation" of the conflict, Russia's ambassador to Denmark warned on Monday.

Denmark and the Netherlands on Sunday announced they would provide the advanced jets to strengthen Kyiv's Soviet-era air force, as it pursues a grinding counteroffensive against Russian forces in the east.

During a visit by Ukrainian President Volodomyr Zelensky to Denmark on Sunday, Danish Prime Minister Mette Frederiksen said her country would deliver 19 of the jets, six of them by the end of this year, eight next year and five in 2025.

"The fact that Denmark has now decided to donate 19 F-16 aircraft to Ukraine leads to an escalation of the conflict," Russian ambassador to Denmark Vladimir Barbin said in a statement to the media.

Russian Foreign Minister Sergei Lavrov said in July that Moscow would consider the F-16s a "nuclear" threat because of their capacity to carry atomic weapons.

"By hiding behind a premise that Ukraine itself must determine the conditions for peace, Denmark seeks with its deeds and words to leave Ukraine no choice but to continue the military confrontation with Russia," Barbin said.

"Such a position pushes Ukraine into the abyss and condemns its people to new victims."

Washington had announced its approval of the F-16 transfers on Friday.

Agence France-Presse