An advocacy group in Nebraska said it was calling on U.S. regulators to shut down the Keystone oil pipeline following a spill from TransCanada's system.

"We cannot accept this continued endangerment of our land and water," a statement from advocacy group Bold Nebraska read.

TransCanada said about 400 barrels of oil spilled from the Keystone artery in South Dakota. The system was shut down briefly after the release was discovered April 2. According to the narrative provided by Bold Nebraska, an area farmer found the leak before TransCanada's systems were triggered.

According to the terms of an order from the federal Pipeline and Hazardous Materials Administration, the company restarted the pipeline during the weekend at a reduced rate. The PHMSA said it was investigating the cause of the leak and would consider formal penalties or charges if the company is determined to have violated any pipeline standards.

Bold Nebraska said the April 2 spill was the 30th spill from the Keystone system since it launched in 2010.

Initial estimates put the size of the release in South Dakota at about 125 barrels.

"We call on federal and state authorities to shutdown TransCanada's Keystone pipeline and conduct an immediate review of the entire pipeline's integrity," the advocacy group said.

Bold Nebraska in 2014 pressured pipeline planner TransCanada to revise the Keystone XL route through the state to avoid the Sandhills area. A permit to build Keystone XL, an extension of the original pipeline, was denied by the U.S. government in November on environmental grounds. TransCanada in January launched a legal challenge against the decision.