Environmental activists protesting the Keystone XL pipeline project in front of the White House, August 20 , 2011
The US police have arrested dozens of environmental activists who staged a sit-in in front of the White House to protest a plan to build a pipeline which is believed to cause serious environmental damages in America.

Around 2,200 people from all over the US are expected to take part in the two-week event which began on Saturday, AFP reported.

The protest is designed to pressure US President Barack Obama to deny permit for the USD 13 billion Keystone XL pipeline project, which is planned to stretch 1,700 miles from Canada to the US Gulf Coast.

Environmental experts say the project requires energy that produces a large volume of greenhouse gasses.

"President Obama can stop this climate-killing disaster with the stroke of a pen," said Bill McKibben, spokesman for Tar Sands Action, the environmental group that organized the protest.

"This is the most important environmental test that President Obama has faced. He has to decide whether or not to grant permission for this giant pipeline," he added.

The sit-in comes as the US chief executive is on vacation despite the economic hardship of the country and at a time when 14 million Americans are out of work.

The US government is expected to announce its decision by the end of 2011 whether to grant permit to the proposed pipeline project.

The pipeline proposed by TransCanada would begin in Alberta in western Canada and pass through the US states of Montana, South Dakota, Nebraska, Kansas and Oklahoma before ending up in Texas at the Gulf of Mexico.