Ukraine may not be able to retake all Russian-occupied territory by force, the US secretary of state has suggested, in remarks likely to anger Kyiv.

The US is Ukraine’s most important military backer and has pledged to continue its support for “as long as it takes” to defeat Russia. But Antony Blinken told Congress on Thursday that some of Ukraine’s stated war aims might only be possible through diplomacy.

“I think there’s going to be territory in Ukraine that the Ukrainians are determined to fight for on the ground; there may be territory that they decide that they’ll have to try to get back in other ways,” he said when asked whether the US-backed President Volodymyr Zelensky’s goal of liberating Crimea, adding: “These have to be Ukrainian decisions about what they want their future to be and how that lands in terms of the sovereignty, the territorial integrity, the independence of the country.”

The comments underline unresolved tensions between Ukraine and several of its western backers over the possible outcome of the war and especially the status of Crimea.

Russia annexed Crimea during its first invasion of Ukraine in 2014. Ukraine never accepted the annexation but did not attempt to challenge it by force before Russia’s fullscale invasion last year.

Russia considers Crimea sovereign Russian territory, and some fear the Kremlin may consider an attempt to liberate it threatening enough to warrant the use of nuclear weapons.

Since September, Russia has claimed the Donetsk, Luhansk, Kherson and Zaporizhzhia regions of Ukraine. Dmitry Medvedev, the deputy chairman of Russia’s Security Council and an ally of Vladimir Putin, on Friday, said Russia wants to create demilitarised buffer zones inside Ukraine around areas it has annexed.

“We need to achieve all the goals that have been set to protect our territories, that is, the territories of the Russian Federation,” he said.

He added that Russia would have to push further into Ukraine if such zones were not established. Russia currently controls just under a fifth of Ukraine’s territory, including Crimea.

The Daily Telegraph, London