Ukraine's popular ex-defence minister Mykhailo Fedorov has called for wartime elections, in what has been seen as a major challenge to President Volodymyr Zelensky.

The country has been under martial law since Russia launched its full-scale invasion in 2022, meaning elections have been suspended.

"Democracy cannot be held hostage by Russia," Fedorov said in a video posted on Tuesday.

But there are practical concerns as to how free and fair elections could be held in a war-torn nation, which Fedorov has not addressed.

Fedorov has also not confirmed if he would run against Zelensky.

The BBC's Dan Johnson reports from Kyiv.