US President Barack Obama says there is no clear evidence that the shooter in the massacre in Orlando, Florida, was directed externally by a larger terrorist network.
"It appears that the shooter was inspired by various extremist information that was disseminated over the internet," the president told reporters in the Oval Office on Monday after a briefing by senior officials including Federal Bureau of Investigation Director James Comey.
Obama said administration officials were examining various internet sites.
The shooter, Omar Mateen, expressed allegiance to the radical group Islamic State in a call to the city's emergency telephone number during a standoff with police while holding hostages in a nightclub called Pulse early on Sunday.
Obama also said the United States had to think about the risks of firearms laws that allow easy access to powerful guns.
Police have said the gunman was armed with an assault-rifle-type weapon and a handgun that were purchased legally.
Omar Mateen travelled to Saudi Arabia in 2011 and 2012, a Saudi Interior Ministry security spokesman says.
Major General Mansour Turki said on Monday that Mateen performed the umrah Islamic pilgrimage for 10 days in March 2011, and eight days the following March.
A US official said his travel records indicate that he apparently also visited the United Arab Emirates on one of the trips.
Umrah is a lesser pilgrimage to Mecca than the haj, which unlike umrah is mandatory for all Muslims.
However, the official said, the Saudis have so far not provided any evidence that Mateen made contact with known extremists during his visits to the kingdom, adding that anyone thought to be a threat is kept under surveillance by Saudi authorities, although that doesn't mean they have a handle on everyone with radical views or contacts.
Early on Sunday, Mateen stormed the nightclub with a handgun and an AR-15 semi-automatic rifle, fatally shooting 49 people before police killed him in the worst mass shooting in US history.
Fifty-three others were wounded, many critically.
US authorities said Mateen called police during the massacre to pledge allegiance to Islamic State, which in recent years declared a caliphate over large swathes of Iraq and Syria.
But the depth of his commitment to the militant group is unclear.