CAIRO — An Egyptian man stabbed an American man outside the United States Embassy in Cairo on Thursday. It was not clear why.

A spokesman for the embassy, David J. Ranz, said the man who was stabbed was a private American citizen not affiliated with the embassy. Egyptian security forces arrested a suspect, and the victim was taken to a hospital, Mr. Ranz said. He gave no further details about the American’s identity or condition.

The stabbing took place at midday, despite the usual heavy presence of security forces in the area. The security situation in Cairo has deteriorated since the revolution that toppled President Hosni Mubarak in February 2011.

Attacks on Americans remain rare in Egypt, but there are often protests near the embassy that trumpet anti-American sentiments. Last September, hundreds of youths battled security forces around the embassy to express outrage over a video made in the United States and posted online that was seen as mocking the Prophet Muhammad.