“We strongly condemn the terrorist attack today by a Hamas gunman in Jerusalem’s Old City, which killed one person and injured others. We offer our condolences to the victims and their families,” the State Department said in the short statement.
Kay, an employee of the Western Wall Heritage Foundation, was working as a tour guide in the Old City. He was engaged to be married.
A native of Johannesburg, Kay had studied at Rabbinical College of Australia and New Zealand.
Kay will be laid to rest at Jerusalem's Har HaMenuchot cemetery Monday, at a funeral service set to begin at 11:00 a.m.
The attack occurred near the Chain Gate, near the Western Wall.
The terrorist was shot and eliminated by security forces on the scene.
After being wounded in the attack, Kay was rushed to Hadassah Medical Center on Mount Scopus, where he was later pronounced dead.
A preliminary investigation into the attack found that the terrorist opened fire with a submachine gun. A knife was also found on the terrorist's person.
Earlier on Sunday, US Ambassador to the United Nations, Linda Thomas-Greenfield, offered her condolences, tweeting, "Heartbroken by news of the attack in Jerusalem, where I just returned from a meaningful visit. My deepest condolences to the families of those injured and killed."