In a statement condemning the terror attack, the president urged the world to stand up together against all atrocities motivated by a twisted understanding of religion or ideology.
"I join the rest of the world in condemning the terror attack in New Zealand, and sympathize with the families of the dead and wounded, and with the government of Prime Minister Jacinda Arden," he said.
He added: "The attack is a stark reminder of the threat terrorism poses to all the peoples of the world. We must stand up together against all atrocities that are motivated by a twisted understanding of religion or ideology."
At least 49 people were killed and dozens wounded when the gunman, identified as a 28-year-old Australian right-wing extremist, opened fire on worshippers in two mosques.
A video live-streamed by the assailant on Facebook showed him rapidly firing what appeared to be hundreds of bullets at his defenseless victims using various weapons.
New Zealand's prime minister has vowed to toughen the country's gun laws after revealing Saturday that the man charged with murdering 49 people in two mosques legally purchased the arsenal of firearms used in the massacre.
Jacinda Ardern said the gunman, a 28-year-old Australian, obtained a "Category A" gun licence in November 2017 and began purchasing the five weapons used in Friday's attacks in the southern city of Christchurch the following month.
The firearms included two semi-automatic rifles, two shotguns and a lever-action weapon, she said, speaking to reporters in Wellington, before heading to Christchurch.