'We stand with you': Obama visits Orlando to meet shooting victims' families

US President Barack Obama visited Orlando, Florida on Thursday to meet relatives of the people killed by a lone gunman who shot up a gay nightclub in an attack that left 49 dead and wounded 53 more.

Four days after the worst mass shooting in recent US history, Obama made a solemn pilgrimage to meet staff at the Pulse nightclub, emergency responders and some of the dozens of families shattered by gunman Omar Mateen.

During his trip, he urged politicians in Washington to adopt and pass more stringent gun control legislation, and asking them to “end the plague of violence that these weapons inflict on so many lives”.

“Our hearts are broken, too,” Obama told the relatives. 

Directly addressing the LGBT community, he said: "You are not alone. The American people and our allies and friends all over the world stand with you."

Relatives of the victims "don't care about the politics. And neither do I," he said.

“Today, once again, as has been true too many times before, I held and hugged grieving family members and friends and they asked, 'Why does this keep happening?'” 

He and Vice President Joe Biden also placed flowers at a ceremony for the victims of the mass shooting at a memorial at the Dr Phillips Center for the Performing Arts in Orlando on Thursday.

“Those who were killed and injured here were gunned down by a single killer with a powerful assault weapon,” Obama said. “The motives of this killer may have been different than the mass killers in Aurora, or Newtown. But the instruments of death were so similar. Now another 49 innocent people are dead. Another 53 are injured. Some are still fighting for their lives.”

“We can’t anticipate or catch every single deranged person … but we can do something about the amount of damage that they do,” he added.

Mateen - who pledged allegiance to the leader of the Islamic State (IS) group in a 911 call during the attack - was killed in a police raid.

Earlier on Thursday, the owner of a Florida gun shop said his employees had called the FBI to tip off the agency about a suspicious man - who turned out to be Mateen - who came into the store a few weeks before the attack.

Co-owner Robert Abell said Mateen asked for level-three body armour, but was told it was not sold at the store. The man then made a phone call in a foreign language. He later asked to purchase ammunition in bulk, but the workers did not sell it to him, Abell said.

But law enforcement officials told CBS News that they have no evidence the gun shop workers made a phone call to the FBI or local police about Mateen.

The Orlando assault has fuelled America's poisonous partisan culture wars, prompting new salvos in bitter election-year rows about immigration, counterterrorism, LGBT rights and guns.

The Republican-controlled Congress has steadfastly refused to pass any gun legislation, saying to do so would infringe on the constitutional rights of gun owners.

Frustrated Democrats took to the Senate floor Wednesday to launch a procedural obstruction, known as a filibuster, to pressure Republicans to accept so-called "no-fly, no buy" legislation that would bar those on watch lists or no-fly lists from purchasing firearms.

The move was a success, and votes were set for next week.

However, some civil liberties activists feared that dependence on government watch lists for gun restrictions could prove discriminatory and unfair. In fact, the Michigan chapter of the Council on American-Islamic Relations (CAIR) filed a lawsuit against the federal government in April, saying the watch list system disproportionately targets Muslims.

Other efforts for tougher gun laws, such as a wholesale ban on assault-style weapons like the AR-15 used by Mateen, have reached a Congressional stalemate.