US securities regulators have sued Elon Musk for allegedly failing to make timely disclosures on his purchases of Twitter shares in 2022, helping him achieve a discount of at least $150mn on his additional stock acquisitions.

The Securities and Exchange Commission accused Musk, one of president-elect Donald Trump’s closest allies, of not disclosing a holding of more than 5 per cent of Twitter on time, in contravention of US securities law.

Regulators claimed in a civil lawsuit filed in Washington federal court on Tuesday that Musk bought up more than 5 per cent of Twitter stock by March 14 2022, but he publicly disclosed his ownership only on April 4 — 11 days after it became reportable. On the day his stake was reported, Twitter shares rose more than 27 per cent, the SEC said.