* TSX down 137.28 points, or 1.05 pct, at 12,960.54.
* All 10 of the index main groups lower (Updates to afternoon)
By Trish Nixon and Claire Sibonney
TORONTO, June 15 (Reuters) - Toronto's main stock index extended losses on Wednesday, falling back below 13,000, as disappointing U.S. economic data and escalating fears over Greek debt weighed on commodity prices.
Energy shares slipped 1.9 percent and played the biggest role of any sector in leading the market lower. Energy stocks weakened with the price of oil, which fell more than $5 a barrel on the back of a stronger U.S. dollar and patchy U.S. data. [O/R]
Suncor Energy SU.TO was the most influential decliner on the index, down 2.9 percent at C$37.27.
Dampening investor sentiment were reports that showed U.S. consumer prices hit their highest in nearly three years in May and a regional factory gauge contracted this month, suggesting the economy faces a troubling mix of weakness and inflation. [ID:nN15281293]
Financial stocks fell 1.4 percent after Moody's warned that it may review the credit ratings of French banks BNP Paribas, Credit Agricole and Societe Generale for a possible downgrade, citing their holdings of Greek public and private debt. [ID:nL3E7HF0A4]. [MKTS/GLOB]
While Canadian banks have little or no exposure to Greek debt, they often trade in sympathy with their global peers. Toronto-Dominion Bank TD.TO, down 1.7 percent at C$78.26, and Royal Bank of Canada RY.TO, off 1.1 percent at C$53.80, rounded out the top three decliners.
"The overnight news didn't bode well," said Bruce Latimer, a trader at Dundee Securities.
"The market is trying to find a bottom here, a base it can build on, and until the market can absorb bad news its going to drift."
Investors fretted after euro zone finance ministers failed to agree on how to involve private investors in a second financial rescue for highly indebted Greece, which boosted safe-haven government debt of the United States and Germany.
Greece's prime minister offered to quit and make way for a national unity government after mass protests against a new austerity plan turned violent, with the country teetering on the brink of default. [ID:nLDE75E0JC]
At 2:20 p.m. (1820 GMT), the Toronto Stock Exchange's S&P/TSX composite index .GSPTSE was down 137.28 points, or 1.05 percent, at 12,960.54. The retreat cut short Tuesday's 1.22 percent rally.
"We had what can maybe be deemed as a false start yesterday with the equities trying to go a little better," added Latimer.
All 10 of the index's main groups were in negative territory, including weighty materials, which fell 0.4 percent. The sector includes mining stocks.
Bucking the broader trend was the gold subsector, up 0.4 percent.
Gold miners made up four of the top five gainers on the index, led by Goldcorp Inc G.TO, up 2.3 percent at C$46.62, Barrick Gold ABX.TO, up 0.8 percent at C$42.93, Kinross Gold K.TO, up 1.1 percent at C$15.11, and Agnico Eagle AEM.TO, which rallied 1.9 percent at C$60.90.
Air Canada ACa.TO shares, up nearly 7 percent to C$2.02, also helped lead the market higher.
The union representing striking sales and customer service agents at the country's biggest airline said it is determined to reach a contract agreement before the federal government forces employees back to work. [ID:nN15126649]
Poor domestic data did not help investor confidence.
The Japanese tsunami dragged down Canadian manufacturing sales in April and home sales dipped in May, reports on Wednesday showed, offering further evidence the economy hit a soft patch in the second quarter. [ID:nN15282152]
($1=$0.98 Canadian) (Editing by Jeffrey Hodgson)