Secretary of State Rex Tillerson recused himself from having any role in the approval of the Keystone XL pipeline, the State Department said Thursday.

"Secretary Tillerson decided in early February to recuse himself from TransCanada's application for a presidential permit for the proposed Keystone XL pipeline," said Mark Toner, acting State Department spokesman. "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."

The statement came just hours after the activist group Greenpeace sent letters to State Department legal advisers and a top federal watchdog asking that Tillerson be forced to recuse himself because of a conflict of interest.

Tillerson was formerly CEO of oil giant Exxon Mobil, which has a stake in seeing the oil pipeline approved. The pipeline would move crude oil from Alberta, Canada, nearly 1,200 miles southward to refineries on the Gulf Coast.

A major chunk of the pipeline has already been completed in the United States. The State Department must approve the permit to build the segment of the pipeline that crosses the border from Canada into the U.S.

"Rex Tillerson's recusal from the Keystone Pipeline decision might have never been transparent to the public without people flooding the lines of the Office of Government Ethics today," said Greenpeace Climate Campaign Specialist Diana Best. "We must keep pushing this administration into the spotlight and demanding that ethics watchdogs hold these individuals accountable and make these decisions regarding rampant conflicts of interest transparent.

"Greenpeace is also requesting that the Office of Government Ethics make public any information relevant to this decision, including any information about recusals, waivers requested or sought, and further ethics disclosures.

"The people will have to continue to watch Trump's Cabinet of billionaires and corporate executives like hawks. In the meantime, the Office of Government Ethics should consider adding more phone lines."