The price of oil sank some 5 percent as the likelihood of an Iran nuclear deal with the West, which could result in more crude supply on the market, trumped concern over an air strike in Yemen by Saudi Arabia and its allies that could endanger a major oil supply route. [O/R]

"The energy group is again being driven by crude oil ... We had a spike yesterday on geopolitical concerns, but obviously that didn't last today," said Elvis Picardo, strategist at Global Securities in Vancouver.

The overall energy group fell 0.9 percent and a major decliner in the sector was Vermilion Energy Inc (>> Vermilion Energy Inc.), down 2.2 percent at C$54.07.

The Toronto Stock Exchange's S&P/TSX composite index <.GSPTSE> finished the session down 57.38 points, or 0.4 percent, at 14,812.42. Four of the index's 10 main groups, including the heavyweight financials, materials, and energy groups, were in negative territory.

The index was down almost 0.9 percent on the week.

The financial sector was off 0.85 percent. In the group, Fairfax Financial Holdings (>> Fairfax Financial Holdings Ltd), one of the largest shareholders in smartphone maker BlackBerry Ltd (>> BlackBerry Ltd), fell just under 1 percent to C$727.00, and was the most influential decliner on the index.

Royal Bank of Canada (>> Royal Bank of Canada) was down 0.8 percent at C$75.09.

"The banks have been poor performers for a while. People have a negative view of market and they're using them as a source of cash. They're easy to sell, they're easy to buy," said David Cockfield, managing director and portfolio manager at Northland Wealth Management.

"They are economy stocks, and from an economic standpoint, it looks like we're going to have a slow year. But we still like them."

BlackBerry Ltd shares rose 3.4 percent to C$11.99 after the company posted better-than-expected fourth-quarter earnings, though it also posted a much bigger-than-expected decline in revenue.

The materials group, home to mining companies, was off 0.3 percent as gold and copper prices fell.

(Reporting by Solarina Ho Editing by W Simon and Peter Galloway)

By Solarina Ho