JERUSALEM - A drone aircraft that entered Israeli airspace last week was apparently on a mission to take pictures of the Dimona nuclear research center in southern Israel, Israeli officials said.

What the aircraft managed to learn and whether it transmitted its observations to a remote facility were not known. Israeli officials have said the aircraft was launched from southern Lebanon and was shot down "some time" after it entered Israeli airspace. Hezbollah, the Lebanese Shiite militia, says that its technicians assembled the aircraft from parts provided by Iran.

"This was a crude device, but it was a drone with all the capabilities that unmanned aerial crafts offer, and for that reason it is worrying," an Israeli military official said on the condition that he not be identified. "We are studying the drone now to learn more about what it accomplished and what Hezbollah intended with it."

The drone was the third unmanned aircraft Hezbollah has dispatched over Israel. Israeli officials said it was the most sophisticated to date. According to the initial account of its downing, the aircraft entered Israeli airspace from the Mediterranean and traveled about 35 miles before it was shot down. Dimona, where Israel is believed to assemble its nuclear weapons, is about 45 miles from the Israeli coast.

Whatever its mission and capabilities, the drone marked another escalation in Israel's conflict with Iran over Iran's nuclear program. Israel believes Iran is attempting to build a nuclear weapon, a charge Iran denies, and has threatened to bomb that country's nuclear facilities to prevent it from developing the technology to build one.

Whether Iran would contemplate attacking Dimona in response to Israeli actions is unknown, but at a minimum, the presence of an Iranian drone near the nuclear facility would seem to be a taunt that whatever Israel might do, Iran is capable of doing as well.

"It is our right to send other drones whenever we want," said Hassan Nasrallah, the head of Hezbollah. "It was not the first time and it will not be the last."

He said the drone had been designed in Iran and assembled by Hezbollah in Lebanon.

Israeli Prime Minister Benjamin Netanyahu confirmed that Hezbollah was responsible for the drone, telling reporters that Israel would "act with determination to defend its borders at sea, on air and land." He said the drone had "failed on its mission."

The Israeli military official, however, said it was possible that the drone had transmitted imagery of the area around Israel's nuclear research center.