The reason for the attack was not immediately clear, though Egyptian officials said it did not appear to be politically motivated. The victim was rushed to a nearby hospital; his condition was not immediately known.
Embassy officials could not immediately be reached for further details. But an official with
The victim later told investigators that he works at a U.S. research center in Cairo and was waiting to complete paperwork for his wife, said Hamdy Mansour, a senior prosecutor in the capital.
The victim said he was approached by a young man, who asked where he was from. When the victim identified himself as an American, he told investigators, the man stabbed him in the neck, Mansour said.
Police stationed around the embassy apprehended the alleged assailant, who did not have identification documents on him at the time, according to the Interior Ministry official, who declined to be identified.
Mansour said the suspect was being held on charges of attempted murder and possession of a knife.
Though such attacks are unusual, the U.S. Embassy in Cairo has been a focus of anti-U.S. sentiment in the past.
In September, Egyptian demonstrators scaled the walls of the compound and took down an American flag in protest over a video that they said mocked the Muslim prophet Muhammad. That night, an apparently unrelated attack on the U.S. mission in the Libyan city of Benghazi killed the U.S. ambassador there and three other Americans.
Egyptian officials said there did not appear to be a political motive for Thursday's attack.
"He is just an unemployed man with a knife," the Interior Ministry official said of the suspect. "Any further details about him will be announced by the prosecutor's office once they've concluded their investigations."
Mansour agreed that the attack was "criminal" in nature.
Crime rates have soared in Egypt since the overthrow of President
The government's efforts to return security to Egypt's streets have been slow. Making headlines recently have been numerous reports of vigilante-style justice, including two men accused of stealing a rickshaw who were reportedly stripped, beaten and hanged from a tree by their feet by residents in the Nile Delta village of Samanod. Both men died of their injuries.