The index has fallen 3 percent so far this week as oil erased most of last week's four-day rally.

"We're still captive to the oil markets," said Ian Nakamoto, director of research at MacDougall, MacDougall & MacTier.

"It's hard to step up to the plate when every time you step up to the plate you strike out," he added.

The most influential movers on the index included its biggest bank by market capitalization, Royal Bank of Canada (>> Royal Bank of Canada), which fell 1.7 percent to C$70.08, and Manulife Financial Corp (>> Manulife Financial Corp.), which was down 5.2 percent at C$18.21.

The overall financial services group fell 1.6 percent.

The energy group fell 3.5 percent, including a 4.6 percent decline in Canadian Natural Resources (>> Canadian Natural Resources Limited), to C$27.75.

Imperial Oil Ltd (>> Imperial Oil Limited) fell 1.8 percent to C$41.08 after the country's No.2 integrated oil producer and refiner reported a lower-than-expected quarterly profit.

The Toronto Stock Exchange's S&P/TSX composite index <.GSPTSE> closed down 232.11 points, or 1.83 percent, at 12,442.26. Eight of the index's 10 main groups were in negative territory.

It had closed on Friday at 12,822.13, its highest in more than three-weeks.

U.S. crude prices settled at C$29.88, down 5.5 percent, as hopes of a deal to curb one of the worst supply gluts in history continued to fade.

Also weighing on the market has been concern that oil reliant sovereign wealth funds are being forced to sell equity portfolios, according to Nakamoto.

Railway stocks were another drag, including a 4.7 percent decline in Canadian Pacific Railway (>> Canadian Pacific Railway Limited) to C$159.04.

Brookfield Asset Management Inc (>> Brookfield Asset Management Inc) shares fell 2.3 percent to C$40.58 after it withdrew an offer to buy a stake in infrastructure company Invepar.

WestJet Airlines Ltd (>> WestJet Airlines Ltd.) tumbled 11.1 percent to C$16.63 after reporting a smaller-than-expected quarterly profit, hurt by its large exposure to a weakening economy in Alberta.

(Additional reporting by Alastair Sharp; Editing by James Dalgleish and Chris Reese)

By Fergal Smith