The Israeli air force shot down a drone after it crossed into southern Israel on Saturday, the military said, but it remained unclear where the aircraft had come from.
The drone was first spotted above the Mediterranean Sea in the area of the Hamas-ruled Gaza Strip to the west of Israel, said military spokeswoman Avital Leibovich.
It was kept under surveillance and followed by Israeli air force jets before it was shot down above a forest in an unpopulated area near the border with the occupied West Bank.
Leibovich said it was shot down at about 10 a.m. (0700 GMT), after it traveled east some 35 miles across Israel's southern Negev desert.
Defense Minister Ehud Barak praised the interception as "sharp and effective".
"We view with great gravity the attempt to compromise Israeli air space and will consider our response in due course," Barak said in a statement.
Soldiers were searching the area for the remains of the drone, which security sources said most likely did not originate from the Gaza Strip. It was not immediately clear whether it was armed.
On at least one occasion, Iranian-backed Hezbollah, a Shi'ite group in Lebanon, has launched a drone into Israel. And in 2010, an Israeli warplane shot down an apparently unmanned balloon in the Negev near the country's Dimona nuclear reactor.