Work on Brazil's controversial $13 billion Belo Monte mega-dam ground to a halt Monday after protesters torched buildings at three dam construction sites over the weekend, the developer said.

Saturday, "a group of 30 people set fire to prefab structures at the Pimental site. They went into the cafeteria, destroyed everything and robbed the till" before setting it ablaze, said Fernando Santana, spokesman for builders Consorcio Constructor Belo Monte (CCBM).

And late Sunday, groups of 20 people set structures ablaze at Canais and Diques, two other dam construction sites, said Santana.

"On Monday, as a precautionary security measure, all activities were suspended at the construction site," said Santana, suggesting that "vandals" might be trying to derail salary renegotiation under way.

The state-owned Norte Energia hired CCBM to build the dam, which is set to be the world's third largest when it has been completed. Between 12,000 and 13,000 workers at the site on two shifts, Santana said.

The incidents broke out after CCBM proposed a seven percent wage hike to the workers in an area where the inflation rate is at 30 percent, said Xingu Vivo, a non-governmental group opposing the dam.

On October 9 protesters -- 150 natives and local fishermen -- interrupted dam construction, accusing Norte Energia of backtracking on accords signed in June when people occupied the Pimental area for three weeks.

Indigenous groups fear the dam across the Xingu River, a tributary of the Amazon, will harm their way of life. Environmentalists have warned of deforestation, greenhouse gas emissions and irreparable damage to the ecosystem.

The dam is expected to flood some 500 square kilometers (200 square miles) along the Xingu and displace 16,000 people, according to the government, although some NGOs put the number at 40,000 displaced.

The natives want their lands demarcated and non-indigenous people removed from them, as well as a better healthcare system and access to drinking water.

Expected to produce 11,000 megawatts of electricity, the dam would be the third biggest in the world, after China's Three Gorges facility and Brazil's Itaipu Dam in the south.

It is one of several hydroelectric projects billed by Brazil as providing clean energy for a fast-growing economy.

"Avatar" director James Cameron and actress Sigourney Weaver support dam opponents, drawing parallels with the natives-versus-exploiters storyline of their blockbuster Hollywood movie.