The FBI has arrested the wife of the gunman who killed 49 people at an Orlando gay nightclub last year, taking her into custody in connection with the massacre, the US attorney general said on Monday.

"I can confirm the arrest did occur," Attorney General Loretta Lynch told MSNBC on Monday.

"This is a matter that we continue to take very seriously," she said. She noted that it was always the Justice Department's goal to determine if "there is any other accountability that needs to be had in this case."

Noor Salman — the wife of Omar Mateen, who was killed by police during the rampage at the Florida club in June — was arrested at her home outside San Francisco, the New York Times reported, citing an unnamed law enforcement official.

Salman faces federal charges of obstruction of justice, and aiding and abetting the attempted provision of material support to a foreign terrorist organization, ABC News reported, citing the FBI and her lawyer.

Salman, who moved to the San Francisco area after her husband's attack, is expected to appear in federal court on Tuesday. She will then face extradition to Tampa, where she was indicted, ABC reported.

Salman told The New York Times in November, in the presence of her lawyer, that she wasn't aware of Omar Mateen's plans to attack the Pulse nightclub in Orlando last year.

"I was unaware of everything," she said. "I don't condone what he has done. I am very sorry for what has happened. He has hurt a lot of people."

A photo of Omar Mateen taken from his MySpace page. Screenshot/MySpace

The interview Salman gave to The Times differs from the story she told the FBI as they interrogated her in the hours after the attack. She initially told police that she was with her husband when he went to buy ammunition and a holster the night before he carried out the massacre.

Salman, a Palestinian-American who grew up in Rodeo, California, told The Times that Mateen was physically and emotionally abusive, often hitting her and calling her the Afghan word for "slut." A nurse who has researched domestic violence and who evaluated Salman's case after the attack told The Times "she would be totally oblivious to clues that he is getting radicalized or planning anything."

Mateen, a US citizen born in New York to Afghan immigrants, was living in Fort Pierce, Florida, with Salman when he rented a car and drove to Orlando to carry out the attack. He was armed with an assault-style rifle and a handgun that he had legally bought days before.

Noor said Mateen gave her $1,000 the day before the attack for her and their 3-year-old son to go to California, and then didn't come home for dinner.

Law enforcement sources said in the days after the attack that Mateen had gone further than that, adding Salman to his life insurance policy and giving her access to his bank accounts. Those reports have not been confirmed.

Salman, who deleted her social media accounts shortly after the shooting and has since avoided the press, corroborated some preliminary reports in her interview with The Times.

She confirmed that she and Mateen had met online on a dating site called Arab Lounge. She also said that the final text she received from Mateen — just before he was killed in a shootout with Orlando police inside the nightclub — was a question: Had she seen the news?

Salman told The Times she replied that she had not. Mateen then told her he loved her, she said, and that was the last she heard from him.

The shooting at the gay nightclub was the deadliest shooting in US history, with more fatalities than the mass shooting at Virginia Tech in 2007 and the mass shooting at Sandy Hook Elementary School in Newtown, Connecticut, in 2012.

Reuters contributed reporting.