A US singer has apologised after she swore on live TV during a performance of the US national anthem.

Loomis prompted mockery on social media when she performed The Star-Spangled Banner at an independent candidate debate on Wednesday which was broadcast live on TV station C-SPAN.

On Instagram she called the incident a “mishap” and told the team at Free and Equal Elections, who organised the debate: “I’m so sorry, I didn’t mean to mess up the national anthem.”