WASHINGTON (Reuters) - Omar S. Mateen, the Florida resident suspected of killing 50 people at a gay nightclub in Orlando, Florida, called 911 before the shooting and swore allegiance to Islamic State, NBC News said on Twitter.

In a posting on its web site, MSNBC said Mateen swore allegiance to Islamic State leader Abu Bakr al-Baghdadi.

(Reporting by Timothy Ahmann; Editing by Nick Zieminski)