An American man suspected of killing at least 49 people in a gay nightclub in Orlando espoused support for a jumble of often-conflicting organisations, according to the director of the FBI.

As details of the worst mass shooting in US history emerged, FBI Director James Comey said on Monday that the suspect, identified as 29-year-old Omar Mateen, had not only pledged loyalty to the Islamic State of Iraq and the Levant (ISIL, also known as ISIS), but also expressed solidarity with the Tsarnaev brothers who carried out the Boston Marathon bombing and a suicide bomber who died on behalf of the al-Nusra Front, a group at odds with ISIL.

"They're really trying to paint a picture of a confused person, who felt targeted because of his religion," said Al Jazeera's Patty Culhane, reporting from Orlando.

The gunman had called 911 during the attack at the Pulse nightclub early on Sunday to express his allegiance to ISIL.

But Comey - who believed Mateen had "strong signs of radicalisation" - said that in the past few years, the gunman also expressed support for both al-Qaeda and Hezbollah.

READ MORE: Shock and grief after Orlando shooting

The FBI investigated Omar Mateen for 10 months beginning in May 2013 after he was said to have inflammatory remarks in support of terrorists.

Presidential hopefuls weigh in

Comey said investigators introduced him to confidential sources, followed him and reviewed some of his communications, but Mateen claimed that he made the remarks in anger because co-workers were teasing and discriminating against him because he was Muslim.

As to whether the FBI should have done anything differently, Comey said so far he doesn't think so.

US President Obama, meanwhile, said that Matten appeared to be "self-radicalised", and that there was "no clear evidence that he was directed externally" or that the attack on the nightclub was part of a broader plot.

Also on Monday, Hillary Clinton, the US Democratic presidential hopeful, vowed to make stopping "lone wolf" attackers a top priority if elected, saying that while the gunman may be dead, "the virus that poisoned his mind remains very much alive."

She made a sober national security address in Cleveland, and also called for ramping up the US air campaign targeting ISIL.

READ MORE: Who was Omar Seddique Mateen?

She also vigorously called for banning assault weapons, such as one of the guns the Orlando gunman used.

"I believe weapons of war have no place on our streets," she said.

Donald Trump, the US Republican presidential hopeful, blamed "radical Islam" for the attack as he made a speech in New Hampshire.

He also renewed a call for a temporary ban on Muslims entering the US, saying that the current immigration system "does not permit us to protect our citizens".

Banning guns, he added, would not be an effective solution to halting such attacks.

At least 49 people died and 53 were wounded in Sunday's shooting in Orlando with the rampage only coming to an end after perpetrator Omar Mateen was shot dead in a gun battle with police officers.

"This is about hate and discrimination," Sarah Kate Ellis, president of the LGBT advocacy group GLAAD, told Al Jazeera.

"There were over 100 anti-LGBT laws rulings passed this last year and that creates an environment of hate, which leads to discrimination and that turns to violence. This is a cycle we are seeing."

She added that gay nightclubs were unique to the LGBT community, because its members could act without fear or judgment.

"They are our community centres," she said, "where we can organise, talk and connect."