Russian President Vladimir Putin's future in power has become less certain in the aftermath of the country's invasion of Ukraine, a Western official said on Thursday, but it isn't possible to predict when any changes in the Kremlin may occur.

As the first anniversary of Russia's invasion of Ukraine approaches, some in Russia's elite fear the war will drag on, draining lives and resources, and Putin's hopes of burnishing his reputation in Russia have been dashed.

But he remains secure in power, according to five senior Russian sources.

The official said Putin had been in a much more settled political landscape a year ago, before he launched what Moscow calls a special operation in Ukraine, but that was now more uncertain.

"People are talking about succession in a way that they weren't a year ago. But what there isn't, in a place like Russia, is a clear pathway to change," the Western official told reporters, on condition of anonymity.

The official said that it was hard to see Putin losing Russia's presidential elections, due in 2024, if he stood.

But the official added that while they had believed at the time of a constitutional change in 2020 that Putin would stay in power until the 2030s, that now seemed less likely.

"At that point, my own assessment was that there was a political leadership that we would have for the next decade," the official said.

"I think it's much less certain now, but I'm not saying that any change is about to happen imminently," the official added, saying the timing of any change was "impossible to predict."