THE HAGUE, Netherlands — The United States gave 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 are unlikely to affect the war any time soon.

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

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.

Even so, Air Force Gen. James Hecker, commander of U.S. air forces in Europe and Africa, told reporters in Washington he did not expect the F-16s to be a gamechanger for Ukraine. Getting F-16 squadrons ready for battle could take "four or five years," he said.

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

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

"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 training, according to a U.S. administration official who spoke on condition of anonymity.

U.S. national security adviser Jake Sullivan said U.S. Secretary of State Antony Blinken sent a letter to his Dutch and Danish counterparts this week, offering formal assurance that the U.S. would fast-track approval of all requests from third parties to transfer F-16s to Ukraine.

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.