BUENOS AIRES, Aug 28 (Reuters) - Argentina's benchmark stock index fell on Thursday as lower oil prices hit energy-related shares, while bonds eked out light gains for a second straight session due to a government buyback program.
The MerVal index .MERV ended 0.15 percent lower at 1,777.05 points, extending its losses since the start of the year to 17.4 percent. Volume was a meager $14 million.
"The fall in oil prices dealt the MerVal a bad hand because energy-related stocks are heavily weighted in the index," said Jorge Alberti, an analyst at online brokerage Elaccionista.com.
Tenaris (TENA.BA), the world's top producer of seamless steel tubes for the energy industry, shed 0.65 percent to 84.25 pesos per share, while Brazilian state-run energy firm Petrobras (APBR.BA) fell 0.45 percent to 81.5 pesos.
Oil prices fell more than $2 on Thursday after the U.S. government and the International Energy Agency pledged to release emergency stockpiles if Tropical Storm Gustav disrupted U.S. oil output.
Argentine sovereign debt prices rose 0.4 percent on average in local trade, led by a 2.1 percent gain in the dollar-denominated Bonar 2014 ARBODEN14D=RASL.
Trade was cautious ahead of a closely watched buyback auction launched by the government as part of a wider repurchase scheme aimed at buoying debt prices.
It offered to buy up to $49 million in Thursday's auction, but the results of the sale had not been published before the close of the local debt market.
The peso closed unchanged for a third straight session, at 3.0250/3.0275 per dollar ARS=RASL in interbank transactions and 3.0675/3.0700 ARSB= in informal trade between foreign exchange houses due to central bank intervention. (Reporting by Walter Bianchi and Jorge Otaola; Writing by Helen Popper; Editing by Leslie Adler)