TransCanada Corp. said March 24 that the U.S. Department of State has signed and issued a Presidential Permit to construct the Keystone XL Pipeline.

"This is a significant milestone for the Keystone XL project," said Russ Girling, TransCanada's president and chief executive officer in a statement. "We greatly appreciate President Trump's Administration for reviewing and approving this important initiative and we look forward to working with them as we continue to invest in and strengthen North America's energy infrastructure."

Map of Keystone pipeline system.TransCanada says it will "continue to engage key stakeholders and neighbors throughout Nebraska, Montana and South Dakota to obtain the necessary permits and approvals to advance this project to construction."

In conjunction, TransCanada has discontinued its claim under Chapter 11 of the North American Free Trade Agreement (NAFTA) and will end what it calls its "U.S. Constitutional challenge."

The Keystone Pipeline System was commissioned in 2010 and runs from the Western Canadian Sedimentary Basin in Alberta to refineries in Illinois and Texas, and also to oil tank farms and an oil pipeline distribution center in Cushing, Okla.

A planned fourth phase, Keystone XL, drew environmental protest and in 2015 was rejected by then President Barack Obama.

Three phases of the project are in operation. They are:

The Keystone Pipeline (Phase I), delivering oil from Hardisty, Alberta, over 3,456 kilometres (2,147 mi) to the junction at Steele City, Neb., and on to Wood River Refinery in Roxana, Ill., and Patoka Oil Terminal Hub north of Patoka, Ill., completed in June 2010.

The Keystone-Cushing extension (Phase II), running 468 kilometres (291 mi) from Steele City to storage and distribution facilities at Cushing, Okla., completed in February 2011.

The Gulf Coast Extension (Phase III), running 784 kilometres (487 mi) from Cushing to refineries at Port Arthur, Texas was completed in January 2014.