Peru's government has declared a 30-day state of emergency in a highland province after it said two people were killed and dozens of police officers injured in violent anti-mining protests.

Interior minister Wilver Calle told a news conference that 30 police officers were hurt in clashes near Cuzco when protesters hit police with rocks and set fire to pasture.

The protesters claim the Tinaya copper mine owned by Swiss-based Xstrata plc is contaminating local water supplies and sickening farm animals.

Calle announced the deaths but did not explain how they occurred other than to say that police were forced to open fire on protesters in self defence. He said 46 police officers had been hurt in protests on Sunday.

Prime minister Oscar Valdez defended the police use of force, saying the protesters "extremists who are attacking police authority".

Protesters took a prosecutor hostage but the local mayor, Oscar Mullohuanca, said he was later released. In a tweet, the public ministry said one of its vehicles was set ablaze.

The emergency was declared for Espinar province. It puts the military in charge of public order and allows authorities to suspend civil liberties, including the right to assembly.

Xstrata is the world's fourth-largest copper producer and protesters have been blocking highway access to the Tinaya mine for a week, complaining that it is contaminating two rivers.

An environmental study commissioned by the local Catholic church and carried out last August and September allegedly found high levels of arsenic, as well as copper, mercury and other heavy metals in soil and water samples.

Xstrata denies it is polluting.

"The people are incensed for all that has happened. The situation is extremely volatile," said a local priest, Luciano Ibba.

The state of emergency was the second called by the government in the past six months in response to anti-mining protests.

In December, the government imposed an emergency in the northern state of Cajamarca to end violent protests against the $4.8bn (£3bn) Conga gold mining project, Peru's largest such investment.

Work on that project, whose majority owner is US-based Newmont Mining Co, has been suspended pending negotiations over protecting highlands water sources.

Anti-Conga activists say they will renew protests against the project on Thursday unless the government cancels it.

Peru depends on the mining of copper, gold, silver and other minerals for more than 60% of its export income. The industry has been the key to robust economic growth but has alienated many highlands peasants who complain it has contaminated their water supplies.