But the inquiry into the attack on the Pulse gay night club, in which 49 people were killed, is being treated as a terrorist investigation, he added.

The FBI's director said the gunman was radicalised through the internet.

Meanwhile Donald Trump said he would suspend immigration from certain areas of the world to the US.

The presumptive Republican presidential candidate also renewed his call for a temporary ban on Muslims entering the country.

The US authorities say gunman Omar Mateen pledged allegiance to IS shortly before the attack in Florida.

However, the extent of any links to IS remains unclear.

Speaking in Washington, Mr Obama said: "It does appear that at the last minute he [gunman Omar Mateen] announced allegiance to Isil [IS].

"But there is no evidence so far that he was in fact directed.

"This is certainly an example of the kind of home-grown extremism that all of us have been concerned about for a very long time."

The deadliest mass shooting in recent US history ended when police shot Mateen dead. The attack also left 53 people injured.

Orlando Regional Medical Centre said on Monday that a number of the victims being treated there remained critically ill, and five patients were in a grave condition.

(BBC News)