ORLANDO, the United States, June 15 (Xinhua) -- U.S. Federal Investigation Bureau (FBI) said on Wednesday that it is continuing to investigate the Orlando mass shooting incident, which killed 49 people and wounded 53 others in a gay nightclub on early Sunday in Florida.

FBI said the killer's wife, Noor Zahi Salman, has been questioned and may face charges if found there was any wrongdoing.

NBC News reported on Wednesday that before the attack, the gunman's wife feared that Omar Mateen, the gunman, was going to attack a gay nightclub overnight Saturday and pleaded with him not to do anything violent, but she gave no warning to police after he left.

CNN also reported that Salman was with Mateen when he bought the ammunition.

U.S. authorities are now considering filing criminal charges against Salman for failing to report to police before the deadly attack.

Meanwhile, American people raised questions about whether the FBI missed the red flags in previous investigations into Mateen, who called 911 three times and claimed allegiance to IS, a radical Jahadist group based in Syria and Iraq, while carrying out the worst mass shooting in U.S. history on early Sunday in Orlando.

Presumptive Republican presidential nominee Donald Trump on Wednesday renewed calls for surveillance of mosques as part of U.S.  efforts to prevent terrorism in the wake of the nightclub shooting, as the gunman was a U.S.-born Muslim and the son of Afghan immigrants.

U.S. President Barack Obama on Monday termed the Orlando attack as "homegrown extremism" and "an act of terror and hate" and called for tough actions on gun control on Tuesday.

"Enough talking about being tough on terrorism, actually be tough on terrorism. Stop making it as easy as possible for terrorists to buy assault weapons," Obama said.

Though united in grief, horror and outrage, Americans remain deeply divided over the three major issues: gun control, immigration and how to fight terrorism.