Last month, Polish Prime Minister Jaroslaw Kaczynski had said construction would definitely resume on Aug. 1. On Tuesday, however, threatened with an injunction by the European Court of Justice, Kaczynski said the construction would stop until after the court ruling.

He told Polish public radio that his government "needs to show restraint" in the matter.

The Rospuda Valley highway plan -- which is just one section of the planned "Via Baltica" project to improve links between the Baltic states, Poland and the rest of the European Union -- is for a 40-kilometer (25-mile) stretch of road through a protected area of northeast Poland.

The road is also meant to ease the burden of truck traffic on a single-lane highway that runs through the nearby town of Augustow.

Birds versus developers

The European Commission, the EU's executive arm, describes the valley as a "unique wetland system" and says its animal and plant life must be protected; it argues that the planned road would breach the environmental rules of the 27-nation EU.

Polish authorities say they have picked the least-damaging option available and argue that the highway project includes a pillared bridge across the valley instead of a ground road. Environmental campaigners counter that the planners failed to give proper consideration to an alternative route skirting the valley.

The Commission fired a warning shot against Warsaw at the European Court earlier this year. In March, Poland suspended initial work at the site, citing the bird-breeding season as the reason, rather than the legal clash.

Polish authorities had announced that construction would resume on Wednesday. On Tuesday, however, Kaczynski said resuming work at this stage would have a "negative impact" on the Via Baltica project.

"We are going to win this case," Kaczynski told Polish radio. "We are going to stop work now in order to resume it after we've won."

Work will meanwhile continue on uncontested parts of the Via Baltica, he said. Poland hopes to get almost 481 million euros ($657 million) in EU funds for the Via Baltica, but the money could be in jeopardy if Warsaw breaches EU environmental rules.

Legal threats

Commission environmental spokeswoman Barbara Helfferich said Brussels was waiting for Warsaw to put in writing its pledge to freeze construction in the Rospuda Valley.

"Nothing will happen until the Polish government gives official confirmation," she told AFP news service.

"Then we will need to analyze it to see if there are sufficient guarantees to enable us to withdraw our legal action," she added.

If the case goes ahead, there is no deadline for a ruling, said European Court spokesman Chris Fretwell.

Locals start to protest

Greenpeace, which is also opposed to the project, set up camp briefly at the construction site earlier this year. Environmental activists pitched tents there again on Monday, but decided to leave on Tuesday morning.

Brussels and green groups argue that the construction would damage important nature sites, which are home to the world's only population of aquatic warblers, as well as rare eagles, lynx, wolves and wild orchids.

The Rospuda project has been in the pipeline for 15 years, however, well before Poland joined the EU in 2004. Many residents of Augustow are exasperated by the delays.

On Wednesday, some 50 Augustow residents picketed the headquarters of the European Commission and Greenpeace to protest the halt to motorway construction. And Monday, hundreds of angry Augustow residents set up a blockade in the town, halting truck traffic and causing a huge traffic jam.

Poland's current single-lane Route Eight, the main highway to and from Lithuania, cuts through the center of the town of 30,000 people. Many locals say they can no longer stand the noise, pollution and risk of fatal accidents caused by the 4,500 heavy goods vehicles that rumble through every day.