Iran has slammed the terrorist mass shooting in the US city of Orlando, reaffirming the necessity of launching a firm campaign against the scourge of terrorism.

“The Islamic Republic of Iran, in line with its principled policy in condemning terrorism and its strong determination to firmly and decisively counter this ominous phenomenon, denounces the recent terrorist attack in US [city of] Orlando,” Iranian Foreign Ministry spokesman, Hossein Jaberi Ansari, said on Monday.

Investigators work on the scene following a mass shooting at the Pulse Club in Orlando Florida, US, June 12, 2016. © Reuters

In the deadliest mass shooting in the United States and the nation's worst terror attack since 9/11, an American-born man who had pledged allegiance to the Daesh terrorist group killed 50 people at the Pulse Club in Orlando, Florida, on Sunday. At least 53 others were also injured in the shooting.

FBI agents investigate near the damaged rear wall of the Pulse Club after a mass shooting killed 50 people on June 12, 2016 in Orlando, Florida. © AFP

The gunman, Omar Mateen, 29, took hostages at the club and barricaded himself in the complex but was later killed by specially trained SWAT units.

Daesh later claimed responsibility for the attacks, according to media outlets affiliated with the terror group.