BEIRUT, Oct 10 (Reuters) - Israeli troops opened fire at three positions held by U.N. peacekeepers in southern Lebanon on Thursday, according to a U.N. source who was not immediately able to specify the type of fire.

The source said one of the locations fired at was UNIFIL's main base at Naqoura. There was no official statement from UNIFIL or immediate comment from the Israeli military.

UNIFIL had said on Sunday that it was "deeply concerned by recent activities" by the Israeli military near a peacekeeper position in southwestern Lebanon.

In a letter to Israel's military dated Oct. 3 and seen by Reuters, UNIFIL had objected to Israeli military vehicles and troops positioning themselves "in immediate proximity" to U.N. positions, "thereby endangering the safety and security of UNIFIL personnel and premises".