Nine winners of the Nobel Peace Prize, including Archbishop Desmond Tutu and the Dalai Lama, have written a letter to U.S. President Barack Obama asking him not to approve a pipeline that would ship oilsands crude from Alberta to Texas.

"We urge you to say 'no' to the plan proposed by the Canadian-based company TransCanada to build the Keystone XL, and to turn your attention back to supporting renewable sources of energy and clean transportation solutions," said the letter, which was released Wednesday.

Obama himself won the Peace Prize in 2009 and former vice-president Al Gore shared the award in 2007.

The letter sprang from the U.S.-based environmental organization Natural Resources Defense Council contacting an Ottawa-based group that represents the seven living female winners of the Nobel Peace Prize.

"NRDC and the tarsands coalition people had asked us if we could help," said Rachel Vincent of the Nobel Women's Initiative.

"We thought, 'What can we do? We can send a letter to Obama and express our strong solidarity with those people who are rejecting the pipeline.' Then we reached out to other Nobel Peace laureates, who enthusiastically embraced the letter."

Along with Tutu and the Dalai Lama, the signatories are: Mairead Maguire, Betty Williams, Adolfo Perez Esquivel, Rigoberta Menchu Tum, Jose Ramos-Horta, Jody Williams and Shirin Ebadi. The laureates are from Ireland, Argentina, South Africa, Tibet, Guatemala, East Timor, the United States and Iran.

The letter reiterates arguments made by protesters who have gathered in front of the White House in recent days to try to pressure Obama to reject the $7-billion project. More than 1,200 people have been arrested.

The U.S. State Department recently released its final environmental analysis of the pipeline and determined there would be no significant impact on the six states it traverses.

Canadian environmental activists plan to hold their own protests against the pipeline on Parliament Hill on Sept. 26.

Vincent said the laureates who signed the letter are well aware of the issues over the pipeline and the extent of opposition to it.

"All of the signatories to the letter are people who have strong concerns around the pipeline and in general around climate change," she said.

"Climate change is a global issue. That is why having a group of Nobel Peace laureates speak out on the issue is a perfectly valid thing to do."

One member of the Nobel Women's Initiative — 2004 winner Wangari Maathai of Kenya — did not sign the letter. Vincent said Maathai didn't think she knew enough about the issue to take a public stand.

Pipeline opponents say it would present a hazard to the land and groundwater it passed through. They also say it would lock the U.S. into Alberta's oilsands as a major energy source at a time when the government should be doing what it can to encourage renewable energy.

TransCanada spokesman Terry Cunha pointed out the State Department's environmental analysis found the pipeline's chosen route would disturb the least amount of land of any of the available routes. It also concluded the Keystone pipeline would be built to a higher degree of safety than existing pipelines and that the material it carried wouldn't have characteristics that could corrode the pipe faster.

Travis Davies of the Canadian Association of Petroleum Producers said the letter is based on politics, not facts.

"Given energy demand growth, we are going to need more energy from all supply options," he said.

"This is not about Canada's oilsands, or even the pipeline. It's about the desire and belief of some that the world can and should be off hydrocarbons in the very near future."