Salman Rushdie is attacked onstage in Western New York.

Mr. Rushdie had just come onstage and was seated in a chair as a staff member introduced him, when the assailant rushed the stage and assaulted the author. It was not immediately clear whether Mr. Rushdie was injured.

Mr. Rushdie spent about 10 years under police protection, living in hiding after Ayatollah Ruhollah Khomeini, the Supreme Leader of Iran after the 1979 Iranian Revolution, called for his execution in 1989 because his novel “The Satanic Verses” was considered offensive to Islam. The book was banned in India, where he was born, and he was barred from the country for more than a decade.

“There was just one attacker,” said Elisabeth Healey, 75, who was in the audience. “He was dressed in black. He had a loose black garment on. He ran with lightning speed over to him.”

Multiple witnesses said the attacker was able to reach Mr. Rushdie easily, running onstage and approaching him from behind.

Several audience members said they were surprised by how easily the assailant reached Mr. Rushdie.

“There was a huge security lapse,” said John Bulette, 85, who witnessed the attack. “That somebody could get that close without any intervention was frightening.”

“The Satanic Verses” was considered blasphemous by some Muslims because it fictionalized part of the life of the Prophet Muhammad. Ayatollah Khomeini issued a fatwa in 1989 ordering Muslims to kill Mr. Rushdie.

The Iranian government publicly backed the fatwa for 10 years, until at least 1998, when Iran’s president, Mohammad Khatami, said Iran no longer supported the killing. But the fatwa remains in place, reportedly with a bounty attached from a semi-official Iranian religious foundation of some $3.3 million as of 2012.

That year, Mr. Rushdie published a memoir, “Joseph Anton,” about the fatwa. The title came from the pseudonym he used while in hiding.