Brazil plans to protect a huge swathe of the Amazon after the murder of a US-born missionary who had campaigned for the forest's peasant farmers.
Dorothy Stang spent decades defending Para's peasant settlers
Nearly four million hectares (10 million acres) in Para state will become a conservation area in a bid to ward off loggers and landowners.
The government will also reinforce the environmental police force.
Jungle troops have begun flying into Para to help track down Sister Dorothy Stang's killers and restore order.
Helicopters ferried 110 soldiers from the 51st Jungle Infantry Division into the small town of Anapu, where they set up camp near the cemetery where the nun is buried.
About 2,000 troops are being deployed in Para after the murder on Saturday - a suspected contract killing by local ranchers.
Police hunting four suspects have a daunting task: the state is twice the size of France.
Thousands of farmers gathered at Dorothy Stang's burial
"The jungle is against us," said police team leader Superintendent Jose Salles.
"We still don't have any concrete clues where these people are."
Three Brazilian activists were also killed in Para this week.
Sister Dorothy, who was a naturalised Brazilian, had complained that the government was not doing enough to stop land-related violence.
Announcing the creation of the new park in the capital, Brasilia, Environment Minister Marina Silva said the country could not "give in to people committing acts of violence".
"The government is putting the brakes on the predators," she said. Officials will also assess if another large strip of land along a federal highway can be protected.
The BBC's Steve Kingstone notes that prominent land reformers are angry that it took the death of a foreigner to force the government into action.
They point out that Para has seen more than 500 land-related killings over the past two decades.
In all but a handful of cases, the crimes went unpunished.
The government's priority now is to avoid any further settling of scores in a region which has been marked by conflict between loggers and wealthy landowners on one side and peasant farmers and environmentalists on the other.
As well as maintaining order, the soldiers will offer support to the police as they try to trace the two hired gunmen accused of Sister Dorothy's murder.