The wife of the gunman who killed 49 people at an Orlando nightclub may soon be charged in connection with the attack, the deadliest mass shooting in modern US history, Fox News has reported.

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Citing an FBI source, FoxNews.com reported that prosecutors had convened a grand jury to investigate Omar Mateen’s wife, Noor Salman.

Omar Mateen’s first wife, Sitora Yusufiy. Photo: AAP

They are seeking to charge her as an accessory to 49 counts of murder and 53 counts of attempted murder and failure to notify law enforcement about the pending attack and lying to federal agents, according to the report.

NBC News also reported that authorities were considering criminal charges against Noor for failing to come forward with what she knew before the brutal attack. However, no decision has been made on whether to proceed, and that Noor was cooperating with investigators.

Noor has told federal agents that she tried to talk her husband out of carrying out the attack, but also conceded she once drove him to the Pulse nightclub because he wanted to scope it out

Mateen, who was shot to death by police after a three-hour standoff at the club early on Sunday, called 911 during his rampage to profess allegiance to various militant Islamist groups.

Federal investigators have said he was likely self-radicalised and there was no evidence that he received any instruction or aid from outside groups such as Islamic State. Mateen, 29, was a US citizen, born in New York of Afghan immigrant parents.

– with agencies.