A foreign submarine last week penetrated Israel's territorial waters in the north, departing after the Israeli navy discovered it, the military reported on Monday.
An Israel defense source confirmed the submarine was detected on November 10 some 16 kilometers (10 miles) off Israel's coast, and about 3 kilometers inside the area Israel considers its territorial waters.
Israel dispatched its missile boats to intercept the vessel, an Israeli Defense Forces spokeswoman said.
"As a result of the discovery and monitoring, the submarine left the area," she said.
The Israelis did not identify the submarine but said it belonged to "a friendly country" and bore "no hostile intentions."
Several Western navies, including the United States, Italy and Germany operate submarines in the area, as does Russia, military sources said.
The Israelis were still not sure of the submarine's mission and are considering the possibility it was sent to gather intelligence or check its ability to penetrate another country's waters without being detected.
The incident, the first publicized incursion but not the first to have taken place, occurred three days after an Iranian-supplied Hizbullah drone flew over northern Israel and crashed into the Mediterranean in that area.