Pipeline operator TransCanada on Wednesday offered to re-route its planned Keystone XL pipe to avoid environmentally sensitive areas as it carries oil from Canada's tar sands to US refineries.

The new route was designed based on feedback from Nebraska's environmental department and "extensive" public comment sessions, TransCanada said.

It "reflects our shared desire to minimize the disturbance of land and sensitive resources in the state," Russ Girling, TransCanada's president and chief executive officer, said in a statement.

This latest revision comes after the US State Department requested a new route in November and President Barack Obama denied approval for the $7 billion pipeline early this year.

Republican presidential hopeful Mitt Romney lashed out at Obama's failure to prioritize jobs over the environment and House Republicans also seized on the issue and passed legislation in April mandating construction of the pipeline.

Environmentalists fear an accident would spell disaster for aquifers in central US Great Plains states.

They also oppose the project because exploiting the oil sands requires energy that generate a large volume of greenhouse gases and say a change of the route will not lessen the pipeline's dangers.

TransCanada recently began work on a 485-mile (780-kilometer) pipeline between Oklahoma and the Texas coast that does not require US presidential approval.

The US State Department is currently reviewing the application for a permit to proceed with the 1,179-mile Keystone XL pipeline from Hardisty, Alberta to Steele City, Nebraska and is expected to make a decision early next year.