US billionaire Elon Musk was embroiled in a social media spat with Ukrainian officials including President Volodymyr Zelensky on Monday over his ideas on ending Russia's invasion.

Musk sparked the controversy on Twitter by proposing a peace deal involving re-running under UN supervision annexation referendums in Moscow-occupied Ukrainian regions, acknowledging Russian sovereignty over the Crimean peninsula and giving Ukraine a neutral status.

The Tesla and SpaceX founder created a poll to let his more than 107 million followers vote on the idea.

Zelensky responded with a Twitter poll of his own, asking: "Which @elonmusk do you like more?" with the options "One who supports Ukraine" and "One who supports Russia".

Kyiv's ambassador to Germany Andriy Melnyk replied bluntly: "My very diplomatic response (to Musk) is to get lost."

Ukrainian presidential aide Mykhaylo Podolyak suggested a "better peace plan" under which Ukraine took back its territories including Crimea, Russia was demilitarised and denuclearised and "war criminals" faced an international tribunal.

Musk later said Moscow could announce a full mobilisation, leading to a "full war" where "death on both sides will be devastating" given Russia's far larger population.

"Victory for Ukraine is unlikely in total war. If you care about the people of Ukraine, seek peace," he wrote on Twitter.

Russian President Vladimir Putin has called on Ukraine to cease hostilities and negotiate after ordering a partial mobilisation to bolster his forces and threatening to use nuclear weapons.

Zelensky has said he will never negotiate with Russia as long as Putin remained its leader.