The Canadian company, TransCanada, has begun construction on the U.S. leg of the controversial Keystone XL pipeline, installing segments in east Texas even as the fate of the pipeline’s northern leg remains in question. Company officials confirmed that work began Aug. 9 on the section of the pipeline that will run from Oklahoma to Texas, just weeks after the U.S. Army Corps of Engineers approved the final construction permit. TransCanada, which ultimately hopes to build a pipeline to carry tar sands oil from Alberta to refineries in Texas, has agreed to relocate the northern section of the pipeline after the Obama administration, citing possible threats to Nebraska’s ecologically sensitive Sand Hills region, rejected a permit for the entire project. If U.S. officials approve the revised northern section of the pipeline, construction could begin in early 2013, a company spokesman said. Pipeline opponents have already launched protests at construction sites in Texas, and say they will stage future demonstrations in an effort to block the pipeline.