U.S. President Barack Obama on Monday called the Orlando shooting in Florida that claimed 50 lives, including the shooter, "homegrown extremism" that the U.S. authorities had been worrying about.

"As far as we can tell right now, this is certainly an example of the kind of homegrown extremism that all of us have been so concerned about for a very long time," said Obama at the White House.

According to Obama, so far there was no "clear evidence" that the gunman in Sunday's massacre at a popular gay nightclub in Orlando, Florida had been directed externally.

"It does appear that at the last minute, he announced allegiance to ISIL," said Obama, referring to an acronym of the extremist group the Islamic State (IS) based in Syria and Iraq. "But there's no evidence so far that he was, in fact, directed by ISIL."

At least 49 people were killed and 53 others wounded, including a police officer, early Sunday in the shooting at the Orlando nightclub. It was the worst mass shooting in U.S. history and the deadliest terror attack since the 9/11 terror attacks in 2001.

Speaking at a briefing in Orlando on Sunday, a local surgeon told reporters that many of those injured were "critically ill as a result of their injuries," suggesting that the death toll could further rise.

The gunman, identified by authorities as Omar Mateen of Port St. Lucie, Florida, was found dead inside the nightclub after a shootout with the police.

Meanwhile, Director of Federal Bureau of Investigation James Comey said on Monday there were strong indications of radicalization by the shooter and of potential inspiration by foreign terrorist organizations.

So far, it remained unknown if Mateen was motivated by the IS, though investigators said he called 911 during the shooting to swear allegiance to IS.

"It is also not entirely clear at this point just what terrorist group he aspired to support," said Comey here at a briefing.

According to Comey, the shooter made three 911 calls, in which he mentioned not just allegiance to IS, but also solidarity with two suspects of the Boston Marathon bombing and a Florida man who died as a suicide bomber in Syria for al-Nusra Front, a group actually in conflict with IS.

"The bombers at the Boston Marathon and the suicide bomber from Florida were not inspired by ISIL, which adds a little bit to the confusion about his motives," said Comey.

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source : xinhua