The leader of Romania's main opposition party, Victor Ponta, on Thursday pledged to block a Canadian gold mine project in the northwest of the country if he becomes prime minister.

Ponta's Social-Democrat Party (PSD) and its Liberal allies (PNL) are likely to win power in the next election, expected in November, according to opinion polls.

"I will overturn (approval)" if the current government pushs through the Rosia Montana gold mine project, Ponta told foreign reporters in Bucharest.

Rosia Montana Gold Corp., 80 percent owned by Canadian firm Gabriel Resources and 20 percent by the Romanian state, plans to use cyanide to extract some 300 tonnes of gold in the village of Rosia Montana, thought to hold Europe's largest single deposit.

The company still needs the go-ahead from the environment ministry to start digging.

The project has been attacked by environmentalists, archaeologists, historians and international organisations who claim the mine would threaten the environment and priceless Roman-era mining galleries.

The Canadian company plans to invest $1.7 billion (1.2 billion euros) to extract 300 tonnes of gold and 1,700 tonnes of silver over 16 years and says the mine will respect all European standards on environmental protection.

Ponta said he thought the whole project is "about speculation on the stock exchange," adding that he had tabled an amendment to a controversial draft law allowing private mining companies to expropriate land.

The draft law, proposed by an MP belonging to Ponta's own party, has been denounced by rights groups as a helping hand for RMGC, which still needs to buy the land.

"I have put an amendment stipulating that this law will only apply to coal extraction," Ponta said. The bill still awaits parliament's approval.

Ponta charged that the RMGC "has supporters in every political party in Romania because of its very aggressive lobbying."