Obama to console grieving families in Orlando
People embrace during a vigil in Orlando for the mass shooting victims at the Pulse nightclub (AFP Photo/Brendan Smialowski)

President Barack Obama will offer his support to grieving relatives when he visits Orlando Thursday in the aftermath of a mass shooting at a gay nightclub.

Obama, traveling with Vice President Joe Biden, will offer his condolences to the families of 49 people killed in Sunday's massacre at the Pulse nightclub in the central Florida city. Another 53 people were wounded.

The White House said Obama will also meet with emergency medical crews and hospital staff who worked tirelessly to save lives in the chaotic hours after the massacre by gunman Omar Mateen, who was killed when police stormed the club.

Mateen, a Muslim American of Afghan origin, in a 911 call during the attack pledged allegiance to the leader of the Islamic State group.

IS then claimed responsibility for the shooting, the worst in modern US history. FBI agents believe that Mateen was radicalized by following extremist propaganda online.

However witnesses also say Mateen was a regular at the gay club and used gay dating apps.

"This will be, I think, an emotional trip," White House spokesman Josh Earnest said Wednesday.

Separately Orlando is reeling from the murder last week of a young female singer who competed on TV reality show "The Voice," and the death Wednesday of a toddler in an alligator attack at a Disney resort hotel.

- Threats against Muslims -

US authorities have warned that threats against Muslims would not be tolerated, and could be prosecuted, after alleged incidents following the massacre.

"Civil rights violations are a priority for the FBI," assistant special agent Ron Hopper told reporters.

"We will investigate reported incidents against individuals based upon any class, any protected class, to include race, religion, and sexual orientation."

In most cases, making these threats "is illegal," said US attorney Lee Bentley. "Any threats like this detract from what we're doing in law enforcement."

Members of the small Muslim community in Mateen's hometown of Fort Pierce say they have endured profanity-laced taunts and even death threats in recent days.

- Grief counseling -

As Orlando prepares to receive Obama, the process of saying goodbye to the dead began.

The first wake was held Wednesday for a 40-year-old man named Javier Jorge Reyes. More wakes and funerals are expected in coming days.

A new family assistance center opened in Orlando Wednesday in a part of the stadium once known as the Citrus Bowl.

Sarita Figueroa, the director of readjustment counseling services for the Department of Veterans Affairs, explained that her personnel were helping those in need of trauma and grief counseling.

"This is for the community," Figueroa told AFP, adding that counselors had come from across the country.

For relatives of the dead, the aftermath is "very difficult. It's too fresh," she said.

"Some are still getting belongings from that night that were on the floor. Glasses, watches, a wallet... You receive the news that you lost someone, and then you receive the note that you need to go and pick up things. That's another process."

- What did the wife know? -

Mateen's motives for carrying out the slaughter remain unclear.

"He appears to have been an angry, disturbed, unstable young man who became radicalized," said Obama.

US media outlets, citing unnamed law enforcement officials, reported that Mateen's 30-year-old wife Noor may have had prior knowledge of her husband's plan and could face criminal charges.

CNN said Wednesday that federal prosecutors planned to present evidence to a grand jury, including that she accompanied Mateen to the gun store and the club on what may have been a mission to plan the attack.

The woman claims she tried to talk her husband out of the attack and did not know of a specific plot, CNN said, citing unnamed law enforcement officials.

On Wednesday, authorities refused to comment on their talks with her.

"With respect to the wife, I can tell you that is only one of many interviews we have done and will continue to do in this investigation," Hopper said.

Mateen's ex-wife, Sitora Yusufiy, has said he used to beat her.