Orlando gunman Omar Mateen apparently made a series of Facebook posts and searches before and during his attack on a gay nightclub, raging against the “flithy ways of the west” and blaming the US for the deaths of “innocent women and children”, according to a Senate committee letter released on Wednesday.

The killer whose rampage left 49 people dead also searched for “Pulse Orlando” and “Shooting” online on the morning of the carnage on Sunday and said on Facebook: “America and Russia stop bombing the Islamic state,” according to the letter.

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The Senate Homeland Security Committee sent the letter to Facebook chief executive Mark Zuckerberg, asking the company to produce information on Mateen’s online activity and to provide a briefing to the panel.

In its letter, the committee said staffers have learned that five Facebook accounts were associated with the 29-year-old American-born Muslim.

“The real muslims will never accept the filthy ways of the west,” Mateen wrote, according to the letter from committee chairman Senator Ron Johnson.

As he did in his call to a 911 operator during the massacre, Mateen pledged his allegiance on Facebook to the leader of the Islamic State and, in his final post, warned “in the next few days you will see attacks from the Islamic state in the usa”.

Despite his professed loyalty to the extremist group, the Obama administration has said it has seen no evidence that the shooting rampage was directed by IS.

The three-hour rampage began at 2:00am on Sunday and ended with Mateen being killed by a police SWAT team.

The FBI said it is still gathering evidence at the Pulse and analysing mobile phone location data to piece together Mateen’s activities leading up to the massacre, while also interviewing people who had any dealings with him.