The energy group fell 3.7 percent, as U.S. crude fell to a three-month low below $43 a barrel amid worries about a global supply glut and economic headwind.

The most influential weights on the index included its biggest oil and gas producers, with Canadian Natural Resources Ltd (>> Canadian Natural Resources Limited) shedding 4.4 percent to C$39.74 and Suncor Energy Inc (>> Suncor Energy Inc.) falling 3.3 percent to C$34.82.

"Until someone or something can make me understand why oil will go back to $60, $70, $80 a barrel I'm staying clear," said Allan Small, a senior investment advisor at HollisWealth.

Major gold miners also moved lower, with Barrick Gold Corp (>> Barrick Gold Corp.) down 3 percent at C$26.21 and Agnico Eagle Mines Ltd (>> Agnico Eagle Mines Ltd) off 4.1 percent at C$67.78, as the price of bullion retreated ahead of central bank meetings in the United States and Japan.

The materials group, which includes precious and base metals miners and fertilizer companies, lost 1.9 percent.

The world's major economies pledged at a G20 meeting this past weekend to use all policy tools available to boost growth.

The Toronto Stock Exchange's S&P/TSX composite index <.GSPTSE> ended down 102.56 points, or 0.70 percent, at 14,498.10. The index notched its highest close in a year on Friday.

Six of the index's 10 main groups finished in negative territory and there were two falling stocks for every gainer.

The most influential gainers on the index included Canadian National Railway Co (>> Canadian National Railway Company), up 0.9 percent at C$83.99.

The railway reported slightly lower earnings after the bell as a decline in shipments cut into revenue, but said it expects volumes to improve in the months ahead.

Rogers Communications Inc (>> Rogers Communications Inc.), which reported strong earnings last week, added 1.7 percent to C$57.80.

(Editing by Sandra Maler)

By Alastair Sharp