"Contracts are signed and these are long-term contracts and they can be adjusted. However, any change must be made with the agreement of the parties. Changes cannot be unilaterally imposed like they did in Bolivia," he said, adding he doesn't think Peru will follow Bolivia's path.

Humala, however, has given special emphasis to the natural resources sector, with its heavy foreign ownership, saying that resource-extraction companies should pay a windfall tax on profits.

His party's governing plan says that strategic activities such as energy, hydrocarbons, and electricity will be at the service of the nation and of Peruvians. "In this strict sense they will be nationalized," the plan says.

But Humala says that nationalization doesn't mean expropriation, saying instead that the state has different alternatives for taking control, including the introduction of a so-called "golden share." These shares have been used in other countries, and usually provide the government with certain veto rights in strategic company decisions.

The 43-year-old ex-army officer also says that mining companies must pay all outstanding royalties and taxes, threatening to review their contracts if they don't pay.

He has also criticized the nation's constitution for favoring foreign investors over locals, and said it should be changed to allow the state a greater role.

More recently, Humala has said foreign companies would be welcome to invest in exploration and if they find petroleum then the state would take its share, paying for part of the exploration costs.

Humala has the backing of Venezuela's socialist President Hugo Chavez and is close to Bolivia's President Evo Morales, who last week nationalized Bolivia's gas and oil industry.