The US State Department, tasked with deciding on a controversial giant pipeline between the United States and Canada, faced fresh charges Thursday of bias over the project.

The environmental group Friends of the Earth (FoE) cited new emails obtained through the Freedom of Information Act to show what it said is a degree of complicity between US diplomats and pipeline operator TransCanada Corps.

"State Department officials acted as though they were on the same team as TransCanada, rather than meeting their obligation to be independent regulators," FoE climate and energy director Damon Moglen said in a statement.

Friends of the Earth said the documents "suggest State and TransCanada may have been coordinating on media strategy" over the Keystone XL pipeline, which would bring petroleum from Canada's western oil sands through US states to refineries along the Gulf Coast.

It said they indicate the State Department's Matthew McManus saw a meeting with TransCanada as a chance to "be able to address the Nebraska/water issues with one voice," faced with Nebraskans' concerns over wetlands in the US state.

It said the documents show that State Department official Michael Stewart took a tour of the pipeline's "control room in Calgary with a TransCanada executive and in turn advocated high-level access for that executive."

In October, FoE alleged that previous emails it obtained through the Freedom of Information Act showed that State Department employees held a "pro-pipeline bias and complicit relationships with industry executives."

After a group of US lawmakers echoed those concerns, the Office of Inspector General earlier this month launched a probe into how the State Department is handling a pending decision on whether to grant a permit for the pipeline.

On November 10, the State Department said it would study an alternate route for the pipeline, and pushed back its final decision on the project until 2013 -- after next year's presidential elections.

The original decision was to have been made by the end of this year.

TransCanada Corp. then said Monday it would back the rerouting of the pipeline, whose original route was to stretch 1,700 miles (2,700-kilometers).

The company said it supported legislation in Nebraska that would ensure the Keystone XL pipeline does not pass through the state's Sand Hills area, which features important wetlands and a sensitive ecosystem.