Pope Francis has condemned the easy availability of guns following the Orlando massacre on Sunday, the deadliest shooting in American history.

Francis told the audience at a United Nations World Food Program event it was a "strange paradox" that while "forms of aid and development projects are obstructed by involved and incomprehensible political decisions, skewed ideological visions and impenetrable customs barriers, weaponry is not."

"It makes no difference where arms come from – they circulate with brazen and virtually absolute freedom in many parts of the world," he said.

Francis did not mention American gun laws specifically, speaking instead about the international availability of weapons.

His comments follow a statement released by the Vatican expressing the Pope's "deepest feelings of horror and condemnation" over the shooting at a Florida nightclub that killed 49 people and injured 53.

"The terrible massacre that has taken place in Orlando, with its dreadfully high number of innocent victims, has caused in Pope Francis, and in all of us, the deepest feelings of horror and condemnation, of pain and turmoil before this new manifestation of homicidal folly and senseless hatred," the statement said.

"Pope Francis joins the families of the victims and all of the injured in prayer and in compassion. Sharing in their indescribable suffering he entrusts them to the Lord so they may find comfort.

"We all hope that ways may be found, as soon as possible, to effectively identify and contrast the causes of such terrible and absurd violence which so deeply upsets the desire for peace of the American people and of the whole of humanity."

Omar Mateen, 29, has been named as the gunman in the attack. He was killed by SWAT police members when they entered the building.