I don't care about politics: Obama

President Barack Obama travelled to grief-stricken Orlando Thursday, meeting loved ones devastated by a shooting rampage and using his bully pulpit to demand that the Republican-controlled Congress pass gun control.

Four days after the worst mass shooting in 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.

Forty-nine people were killed and 53 wounded when the 29-year-old Mateen -- a Muslim American of Afghan descent -- ran amok in a packed gay nightclub early Sunday, armed with a legally bought assault rifle.

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

But his assault has fuelled America's poisonous partisan culture wars, prompting new salvos in bitter election-year rows over immigration, counterterrorism and guns.

After meeting the victims' families, Obama said "our hearts are broken too" and insisted the tone of the country's hyper-partisan debate on firearms "needs to change."

Relatives of the victims "don't care about the politics. And neither do I," he said. Obama insisted the military would tackle the Islamic State group, al-Qaeda and other extremist groups in their hideouts, and intelligence services would work to disrupt such networks.

But, he warned, the government could not catch every "deranged person."

"We can do something about the amount of damage that they do," he said. "Unfortunately our politics have conspired to make it as easy as possible for a terrorist or just a disturbed individual like those in Aurora and Newtown to buy extraordinarily powerful weapons and they can do so legally."

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.