The Hague. The United States has given its approval for the Netherlands and Denmark to deliver F-16s to Ukraine, officials in Washington and Europe said Friday, in a major gain for Kyiv even though the fighter jets won’t have an impact any time soon on the almost 18-month war.

It was not immediately clear when the first F-16s might enter the conflict but Ukrainian pilots will first have to undertake at least six months' training on the aircraft, according to officials.

Ukraine has long pleaded for the sophisticated fighter to give it a combat edge. It recently launched a long-anticipated counteroffensive against the Kremlin’s forces without air cover, placing its troops at the mercy of Russian aviation and artillery.

In eastern Ukraine, attack helicopter pilots welcomed the news. They said Russia has a clear advantage in the skies, but the introduction of modern fighter jets could dramatically shift the balance of power Kyiv’s way.

Ukrainian forces supporting infantry are using decades-old Soviet-era models, which are vulnerable to air-to-air missile attacks from Russian fighter jets, Capt. Yevgen Rakita, a spokesman for the 18th Army Aviation Brigade, told The Associated Press.

“A modern war cannot be won without aviation (capabilities),” Rakita said.

In making the decision on F-16 deliveries, Washington aims to ensure warplanes can be provided to Ukraine as soon as its pilots complete their training, according to a Biden administration official who was not authorized to comment and spoke to The Associated Press on condition of anonymity.

The official said U.S. Secretary of State Anthony Blinken sent a letter to his Dutch and Danish counterparts earlier this week, offering formal assurance that the US would fast-track approval of all requests from third parties to transfer F-16s to Ukraine.

Danish Defense Minister Jakob Ellemann-Jensen said Friday the training of Ukrainian pilots is starting this month.

A coalition of 11 Western countries — the Netherlands, Belgium, Canada, Denmark, Luxembourg, Norway, Poland, Portugal, Romania, Sweden and the United Kingdom — pledged in July to train Ukrainian pilots to fly F-16s.

Officials have previously said that Ukrainian pilots will need six to eight months of training.

Denmark will hand over some of its F-16s only after receiving its new F-35 jet fighters. The first four F-35s are due to be delivered on Oct. 1.

Washington's blessing for the plane donations to other countries is needed because the aircraft are made in the United States.

Ukraine's Western allies have at times moved slowly on granting Kyiv the military support it has requested.

President Joe Biden’s authorization last May for allies to train Ukrainian forces on how to operate the warplanes, and eventually to provide the aircraft themselves, was preceded by months of debate in Washington and quiet talks with allies, officials said.

The administration had concerns that the move might escalate tensions with Russia. Also, U.S. officials argued that learning to fly and logistically support the advanced F-16 would be difficult. Eventually, the go-ahead came because the F-16s are required for Ukraine’s long-term security needs.

Though delivery is likely months away, Washington says the F-16s — like the advanced U.S. Abrams tanks — will be crucial in the long term as Kyiv faces down Russia.

Ukraine has been relying on older aircraft, such as Russian-made MiG29 and Sukhoi jets. F-16s have newer technology and targeting capabilities. They are also more versatile, experts say.