(Updates with details on fall in stocks, bonds; adds peso)
BUENOS AIRES, Aug 7 (Reuters) - Argentine stocks sank on Thursday, pressured by losses in international markets and a slide in sovereign bond prices amid growing concerns over the country's financing ability next year, traders said.
The benchmark MerVal index .MERV closed down 2.97 percent at 1,815.98 points, partly dragged down by bank shares, which are major holders of Argentine debt.
"The MerVal's sharp fall was led by banks in light of a drastic drop in bond prices, on a day in which the global context didn't help," said Augusto Farina, trader at Amirante Galitis brokerage.
Banking conglomerate Grupo Financiero Galicia (GFG.BA) led losses, shedding 6.16 percent to end at 1.37 pesos a share.
Trade volume on the overall market was a moderate $35.2 million. Of active shares, 31 rose, 57 fell and 19 were unchanged.
Argentine sovereign debt shed 2.7 percent on average in over-the-counter trade, with the peso-denominated 2033 Discount bond sinking 5 percent.
At the same time, the dollar-denominated Boden 2015 fell 4.4 percent ARRO15D=RRBB.
Traders said Venezuela began selling some of the $1 billion in Boden 2015s it purchased in recent days, which may have sparked a general sell-off.
"Investors are starting to realize how risky next year's financing situation is amid signs of a slowing economy," said Guillermo Curutchet, an analyst at Sudamericana de Finanzas.
The peso currency weakened slightly against the dollar for the third straight session, and traders said the central bank sold some dollars on the cash and futures market to keep the peso from slipping further.
In formal interbank trade, where the central bank regularly intervenes, the peso slipped 0.08 percent to 3.0450/3.0475 per dollar ARS=RASL. In informal trade between foreign exchange houses, as measured by Reuters, the peso weakened by the same percentage to end at 3.0625/3.0650 per dollar ARSB=. (Reporting by Walter Bianchi; Writing by Hilary Burke; Editing by Gary Crosse)