May 8 (Reuters) - Canada's main stock index edged lower on Tuesday as energy shares fell ahead of an announcement by U.S. President Donald Trump later in the day about the United States' commitment to the Iran nuclear deal.
* At 9:46 a.m. ET (13:46 GMT), the Toronto Stock Exchange's S&P/TSX Composite Index fell 20.46 points, or 0.13 percent, to 15,788.17.
* Trump will announce whether he will pull out of the Iran nuclear deal or stay in and work with European allies who have struggled to persuade him that it has successfully halted Iran's nuclear ambitions.
* The energy sector, down 1.9 percent, was the biggest drag on the main index, as oil prices eased from their 3-1/2-year highs.
* Shares of Canadian Natural Resources Ltd fell 1.4 percent, also weighing on the energy group, after Royal Dutch Shell Plc's Shell Gas B.V. said on Monday it was selling its entire stake in Canada's largest independent petroleum producer.
* Also hurting the main index was the materials sector, which includes precious metals miners, as gold slipped on the back of the dollar, which surged to a new 2018 high.
* Six of Canada's 10 main index sectors were in the positive territory.
* Among other stocks, Hudson's Bay Co, up 2.2 percent, is working with investment bankers and consultants to identify deals and new measures to turn around its Lord & Taylor department store chain, sources said.
* Shares of NorthWest Healthcare Properties REIT were trading marginally lower after the Canadian landlord announced a $312 million strategic investment in Australian hospital operator Healthscope.
* The TSX posted five new 52-week highs and two new lows. Across all Canadian issues there were 14 new 52-week highs and six new lows.
* The largest percentage gainer on the TSX was Nevsun Resources Ltd, which rose 20.9 percent after the company on Monday rejected proposal from miners Lundin and Euro Sun to acquire all of Nevsun's shares for ~C$1.5 bln ($1.16 billion).
* Westjet Airline, the largest decliner on the index, reported a first-quarter profit that missed analysts' estimates partly hurt by higher fuel prices, sending its shares down 10.1 percent.
* Among the most active Canadian stocks by volume were Aurora Cannabis, down 0.7 percent, after the company posted its third-quarter results.
* Shares of Nevsun Resources and Canadian Natural Resources were also among the most heavily traded stocks.
* Volume on the TSX index was 20.58 million shares. Total volume on Tuesday was 30.42 million shares.
* Economic data showed Canadian housing starts slowed in April, as expected, as groundbreaking on both detached and multiple unit homes decreased. (Reporting by Amy Caren Daniel in Bengaluru; Editing by Maju Samuel)