U.S. Secretary of State Rex Tillerson has recused himself from issues related to TransCanada Corp.'s application for a presidential permit for the proposed Keystone XL pipeline, the State Department said in a letter to the environmental group Greenpeace.

"In early February, Secretary Tillerson recused himself from working on issues related to TransCanada's application," reads the statement.

"He has not worked on that matter at the Department of State, and will play no role in the deliberations or ultimate resolution of TransCanada's application."

Greenpeace on Wednesday called for Tillerson to recuse himself from matters involving Keystone XL, citing his former position as CEO of Exxon Mobil, and started a petition to ask the U.S. Office of Government Ethics to "publicly urge" for his recusal.

Former Exxon CEO Rex Tillerson MUST recuse himself from Keystone XL. Take action now: <a href="https://t.co/E0mnDNhDVc">https://t.co/E0mnDNhDVc</a> <a href="https://twitter.com/OfficeGovEthics">@OfficeGovEthics</a> <a href="https://twitter.com/hashtag/RecuseRex?src=hash">#RecuseRex</a> <a href="https://t.co/GaW2NIoIvQ">pic.twitter.com/GaW2NIoIvQ</a> —@greenpeaceusa

"If the Keystone XL pipeline is pushed through, Exxon stands to profit," Greenpeace said in its petition.

"Tillerson will act in the industry's best interest — not our country's."

The State Department's acting spokesperson Mark Toner was asked by a reporter earlier on Thursday during a press briefing about Greenpeace's petition and whether Tillerson would divest himself of Exxon stock.

"The secretary made very clear that he was going to comply with federal ethics rules, and he is in the process of meeting the terms of that agreement," Toner said.

Rec'd lots of calls today. <a href="https://twitter.com/StateDept">@StateDept</a> indicates Sec. Tillerson recused from issues related to pipeline application: <a href="https://t.co/2n6wEbgdBJ">https://t.co/2n6wEbgdBJ</a> —@OfficeGovEthics

Tillerson vowed to steer clear of Exxon issues

TransCanada tried for more than five years to build the 1,897-kilometre pipeline, until former president Barack Obama rejected it in 2015.

TransCanada resubmitted its application for the Keystone project in January, after Obama's White House successor, Donald Trump, signed an order smoothing its path.

The line is designed to link existing pipeline networks in Canada and the United States to bring crude from Alberta and North Dakota to refineries in Illinois en route to the Gulf of Mexico.

Exxon has a majority stake in Imperial Oil, a Calgary-based company that operates the Kearl oilsands project in northern Alberta.

Tillerson wrote in a January letter to Katherine McManus, the State Department's deputy legal adviser, that for one year after his resignation from Exxon Mobil, he "will not participate personally and substantially in any particular matter involving specific parties in which I know that Exxon Mobil is a party or represents a party, unless I am first authorized to participate."