* TSX ends down 144.28 points, or 1.1 pct, at 12,939.72
* Index closes at lowest level since Nov. 29, 2010
* Hit by Greek downgrade, slumping commodity prices
* All 10 index sectors weaker (Adds details, commentary)
By Claire Sibonney
TORONTO, June 13 (Reuters) - Toronto's main stock index closed below 13,000 on Monday for the first time since November as a downgrade of Greece's credit rating prompted more economic pessimism and pulled down commodity prices.
Greece's credit rating became the lowest of any country in the world after Standard & Poor's downgraded it by three notches, saying the agency would consider any debt restructuring as a default. [ID:nN13126859]
The news sent oil prices tumbling, with U.S. crude futures ending almost $2 a barrel lower, pushing Toronto's energy shares down almost 2 percent. [O/R]
Oil and gas producer Canadian Natural Resources (CNQ.TO) was the one of the heaviest weights on the index, falling 1.9 percent to C$38.61, while Suncor Energy (SU.TO) dropped 1.3 percent to C$37.59.
Brian Pow, a research and equity analyst at Acumen Capital Partners in Calgary, said the euro zone woes, as well as fears of slowing growth in China, were contributing to investors' anxiety.
"People are just moving their risk capital to safer havens and trying to stand back and see what comes out of this," he said.
"I'm of a view we're in a sideways market so we could possibly go lower but ... as the volumes pick up again and as companies report some of their Q2 numbers later in the summer, I think it will prove that some of this current concern is not needed."
The Toronto Stock Exchange's S&P/TSX composite index .GSPTSE ended down 144.28 points, or 1.1 percent, at 12,939.72, its lowest close since Nov. 29.
The selloff saw the TSX break through key psychological support at 13,000 for the first time since Dec. 1.
"One note of caution is that the selloff has been quite sharp but we are still urging our investors to keep this in perspective," said Elvis Picardo, an analyst and strategist at Global Securities in Vancouver.
Picardo noted that the next key support level for the index is 12,500.
The index has retreated about 10 percent since its 2011 high, reached in March, and is down about 4 percent for the year.
"We still think that there are enough positive drivers to offset some of the downside risks in the near term," added Picardo.
"A lot of this downside action has happened after surprisingly weak data points in the U.S. If the next batch of numbers come in a little better than expected, that could be the trigger for a mini rally."
All of the the index's 10 main sectors were weaker, including financials, which dipped 0.2 percent. Among bank stocks, Bank of Nova Scotia (BNS.TO) was the worst performer, down 1.2 percent at C$56.90.
Heavyweight miners were dragged lower by weaker metal prices. Goldcorp Inc (G.TO) was the index's most influential decliner, losing 2.5 percent to C$45.05. Silver Wheaton SLW.TO plunged 5 percent to C$29.88, and First Quantum Minerals (FM.TO) dropped 1.9 percent to C$117.81. [GOL/]
Among materials, Potash Corp (POT.TO), the world's largest fertilizer company, slumped 1.9 percent to C$52.87.
Shares of Air Canada Inc ACa.TO plunged almost 8 percent to C$1.79 after the union representing the airline's customer service and sales staff set a strike deadline of 11:59 p.m. on Monday.
Bucking the broader trend, TMX Group X.TO rose 0.9 percent to C$43.19 after Maple Group filed a formal C$3.7 billion hostile takeover bid for the exchange operator. [ID:nN13101866]
($1=$0.98 Canadian) (Editing by Rob Wilson)