An F-16 fighter jet pilot. Photo: Isaac Garden / USAF

The United States has approved the transfer of F-16 fighter jets from Denmark and the Netherlands to Ukraine as soon as the pilot training is completed, Reuters news agency has learned.

A US official said Washington had given Denmark and the Netherlands official assurances that the United States will expedite approval of transfer requests for F-16s to go to Ukraine when its pilots were trained.

The two countries, which lead the informal ‘fighter jet coalition’, requested US assurances on the transfer of F-16s.

In a letter to his Danish and Dutch counterparts, US secretary of state Antony Blinken assured them the requests would be approved, the US official told Reuters.

"I am writing to express the United States’ full support for both the transfer of F-16 fighter aircraft to Ukraine and for the training of Ukrainian pilots by qualified F-16 instructors," Mr Blinken said in the letter, a copy of which was seen by Reuters.

The Netherlands operates 24 F-16s suitable for rapid deployment and has an additional 18 F-16s that are not operational but may be assigned to other uses.

Denmark has 43 F-16s, 30 of which are in active service. The country plans to retire F-16s from service by the end of 2025, replacing them with modern F-35As.

"It remains critical that Ukraine is able to defend itself against ongoing Russian aggression and violation of its sovereignty," the letter read, adding that the approval of the F-16 transfer would allow Ukraine to take "full advantage of its new capabilities as soon as the first set of pilots complete their training."

It is not known how many aircraft — and how soon — the Netherlands and Denmark will hand over to Ukraine after the training course.

So far, there have been no clear assurances from the authorities of these countries that they will guarantee the delivery of the fighters to the Ukrainian Air Force.

In May, US president Joe Biden officially confirmed that the US military would start training Ukrainian pilots for the F-16.

Ukraine, which has long been pushing for modern fighter jets, has indicated it needs four squadrons, that is 48 F-16s, to effectively deter Russian aggression.