A BBC spokesperson said on Sunday that the British broadcaster is "urgently looking into" issues raised in the Channel 4 documentary on Russell Brand, which included allegations of sexual assault.

"The documentary and associated reports contained serious allegations, spanning a number of years. Russell Brand worked on BBC radio programmes between 2006 and 2008 and we are urgently looking into the issues raised," a BBC spokesperson said in a statement.

On Saturday, British outlets The Sunday Times, The Times and Channel 4's "Dispatches" published a joint investigation in which four women alleged Brand sexually assaulted them in separate instances between 2006 and 2013. One of the women said she was 16 and Brand was 31 at the time of the alleged assault in London.

Brand preemptively denied the allegations in a video posted to his verified Instagram page, which he shared on Friday before the report was published.

The women chose not to be identified by name in the report, according to The Times. CNN has not been able to independently verify their claims.

Earlier, a BBC spokesman said Brand had left the state broadcasting corporation after a serious editorial breach in 2008, noting, "We hope that demonstrates that the BBC takes issues seriously and is prepared to act."

The BBC spokesman said the organization had "evolved its approach" toward talent and complaints over successive years and had "clear expectations around conduct at work," adding that it would "always listen to people if they come forward with any concerns, on any issue related to any individual working at the BBC, past or present."

Brand has written and spoken extensively about his past treatment for drug and sex addiction, along with mental health issues. He has built a digital platform around wellness in recent years.

"These allegations pertain to the time when I was working in the mainstream, when I was in the newspapers all the time, when I was in the movies. And as I've written about extensively in my books, I was very, very promiscuous," Brand said in his video on Friday. "Now, during that time of promiscuity, the relationships I had were absolutely, always consensual."

The reports did not stop the comedian from continuing to perform, and he appeared on stage at the Troubadour Wembley Park Theatre on Saturday as part of his "Bipolarisation" tour, according to the BBC.