This was the second apology Ora gave this week, after news of her 30th birthday bash broke earlier this week, prompting her to speak out.
Writing on the social media platform Instagram, Ora called the party, which involved around 30 guests, a "serious and inexcusable error of judgement".
"It was a spur of the moment decision made with the misguided view that we were coming out of lockdown and this would be OK," Ora wrote on Instagram.
"I feel particularly embarrassed knowing first hand how hard people have worked to combat this terrible illness.
"Even though this won't make it right, I want to sincerely apologise," she added.
London police confirmed that officers had been called to Notting Hill, where the birthday bash took place, over a breach of Covid-19 regulations.
"Officers continue to assess the allegations and are liaising with the local authority regarding a potential breach of regulations at the premises. Enquiries continue," a Metropolitan police statement said.
The singer of hits that include "Let You Love Me" and "How to Be Lonely" has volunteered to pay a fine.
Police in England can issue fines of up to £10,000 ($13,352, €11,168) for breaches of the lockdown curbs.
England was placed under four weeks of restrictions to stop the spread of coronavirus in November. Individuals were banned from meeting indoors with people from other households.
The lockdown ended on December 2 and was replaced by a tiered system allowing hospitality venues to reopen in certain areas under social distancing rules.
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