Sept 17 (Reuters) - Canada's main stock index fell slightly at the open on Tuesday after energy shares gave back gains following a decline in oil prices fueled by worries over the threat of retaliation for attacks on Saudi Arabian crude oil facilities.
* At 9:30 a.m. ET (1330 GMT), the Toronto Stock Exchange's S&P/TSX Composite index was down 13.01 points, or 0.08%, at 16,738.3.
* The energy sector dropped 0.4%, with U.S. crude prices down 0.9% and Brent crude off 1.5%. (Reporting by Shreyashi Sanyal in Bengaluru; Editing by Maju Samuel)