Canada's main stock index declined Thursday for a third straight day as U.S. political worries weighed on investor sentiment.

The Toronto Stock Exchange's benchmark Standard & Poor's/TSX Composite Index fell 48.57 points, or 0.32 percent to close the day at 15,033.64.

The materials sector, which includes precious and base metals miners and fertilizer companies, lost 0.5 percent as aluminum, copper and other base metals retreated from multi-year peaks.

Base metals fell as some investors locked in profits from a steep rally amid doubts about future demand in top metals consumer China.

The financial sector shares also lost ground, falling 0.4 percent, as a deadly car attack in Barcelona for which Islamic State claimed responsibility helped drive down the yields on safe-haven government bonds.

The energy sector fell 0.3 percent.

The Canadian dollar slipped 0.28 cents to 78.92 U.S. cents. while oil prices inched up 23 cents 47.01 U.S. dollars a barrel and gold prices gained 11.40 to 1,294.30 U.S. dollars an ounce.