Partial transcripts of three conversations that Orlando nightclub gunman, Omar Mateen, had with emergency services during the massacre are to be released.

Mateen paused during the three-hour siege to call 911 dispatchers and post internet messages professing support for the so-called Islamic State.

The partial transcripts of the calls made from inside Pulse nightclub will be released on Monday and will include the "substance of his conversations". However, they will not include Mateen's pledge of allegiance to the so-called Islamic State, US Attorney General Loretta Lynch confirmed.

Speaking on CNN's State of the Union, and ABC's This Week, Ms Lynch said the investigation was focused on building a complete profile of the 29-year-old US citizen born to Afghan immigrants, including what motivated him.

Ms Lynch - who will travel to Orlando on Tuesday to meet with investigators, survivors, and the loved ones of those who died - refused to say whether Mateen's second wife, Noor Salman or anyone else will be charged in connection with the attack.

US officials have said that Ms Salman knew of her husband's plans to carry out the attack in which 49 people were massacred.

Ms Lynch said that the transcripts would be redacted to avoid causing further pain to the victims and their loved ones.

On Sunday evening a vigil will be held at a lakeside park in Orlando with 20,000 people expected to attend.