Ukrainian pilots have started flying F-16s within the country, President Volodymyr Zelensky said on Sunday, confirming the long-awaited arrival of the US-made fighter jets more than 29 months after Russia started its special military operation.

"F-16s are in Ukraine. We did it," Zelensky said in a video posted on social media showing him at an air base addressing and meeting Ukrainian pilots. He was standing in front of two F-16s, and two more flew overhead as he spoke.

The arrival of the jets is a milestone for Ukraine, though it remains unclear how many are available and how much of an impact they will have on the battlefield, Reuters commented.

Although new to Ukraine, the F-16s are actually older jets that have been donated by Western allies of Ukraine. Belgium, Denmark, the Netherlands and Norway have committed to providing Ukraine with more than 60 of them over the coming months, in what could be a slow trickle of deliveries, The Associated Press reported.

US President Joe Biden gave the go-ahead last August for used F-16s to be deployed in Ukraine, though the United States will not be providing any of its own planes.

Russia has vowed to shoot them down.

Ukraine may keep some of the F-16 fighter jets at foreign bases to protect them from Russian strikes, according to a senior Ukrainian military official. Russia has warned that it could consider launching strikes at facilities in NATO countries if they host the warplanes used in Ukraine.

Ukraine has previously relied on an aging fleet of Soviet-era warplanes that are outgunned by Russia's more advanced and far more numerous fleet.

Built by Lockheed Martin, the F-16s had been on Ukraine's wish list for a long time because of their destructive power and global availability.

Talking to reporters at an airfield, Zelensky said Ukraine still did not have enough pilots trained to use the F-16s or enough of the jets themselves.

A US official, speaking on condition of anonymity, told The New York Times about a half-dozen pilots were conducting test flights on as many jets in "uncontested" Ukrainian airspace. He said the Ukrainian pilots were getting acclimated to operations on a small scale and had not yet engaged with the Russians.

Meanwhile, the US is alleged to begin deploying new long-range weapons in Germany starting from 2026. Russian President Vladimir Putin had earlier warned Washington that Moscow would stop implementing its unilateral moratorium on the deployment of medium- and shorter-range strike weapons if US long-range missiles appeared in Germany.

It may come when Russia will need to deploy nuclear missiles in response to Western actions, Russian Deputy Foreign Minister Sergey Ryabkov told Rossiya 1 TV channel on Sunday.

Moscow will not make any unilateral concessions to the West to resolve the conflict in Ukraine, and will not give "handouts, gifts, concessions, or any gestures to appease Washington", he said.