By John Kruzel and Andrew Chung

WASHINGTON The U.S. Supreme Court on Thursday dealt a setback to the Navajo Nation, rejecting its bid to require the federal government to develop a plan to secure water access for the tribe on reservation lands in the parched American southwest.

The justices, in a 5-4 decision authored by conservative Justice Brett Kavanaugh, concluded that an 1868 peace treaty between the United States and the tribe did not require the government to take steps such as assessing the tribe's water needs and potentially building pipelines, pumps and wells.

More than 30% of households on the Navajo reservation currently lack running water, according to the tribe.

Conservative Justice Neil Gorsuch, who has supported Native Americans rights in various cases since joining the court in 2017, dissented from the decision along with the court's three liberal justices.

"The 1868 treaty reserved necessary water to accomplish the purpose of the Navajo Reservation," Kavanaugh wrote in the ruling. "But the treaty did not require the United States to take affirmative steps to secure water for the Tribe."

The treaty, reached three years after the conclusion of the U.S. Civil War, ended two decades of sporadic fighting between the United States and the Navajos and established the Navajo Reservation, which encompasses roughly 17 million acres (6.9 million hectares), largely in the Colorado River Basin.

The treaty secured the right of the Navajos to make use of the land, minerals and water on the reservation, which spans parts of Arizona, New Mexico and Utah.

Gorsuch criticized the ruling for deciding more than what was required by the case. In his dissent, Gorsuch wrote that the Navajos sought simply to identify the water rights that the U.S. government holds in trust on the tribe's behalf.

"The government owes the Tribe at least that much," Gorsuch wrote.

The ruling reversed a decision by the San Francisco-based 9th U.S. Circuit Court of Appeals that had given a green light to the Navajo Nation's lawsuit against the U.S. Interior Department and others seeking to prod the government to develop a plan to secure water for the tribe. The 9th Circuit said that the government had a "duty to protect and preserve the Nation's right to water."

"The Department of the Interior is committed to upholding its trust and treaty obligations to Tribes, as well as to ensuring that water rights for Colorado River users are fulfilled according to the law. We are reviewing the decision," a department spokesperson said in a statement following Thursday's ruling.

The decision follows another ruling this month in which the Supreme Court upheld a decades-old federal law governing Native American adoption and foster care placements, throwing out a challenge brought by the state of Texas and other plaintiffs to standards that give preferences to Native Americans and tribal members.

(Reporting by Andrew Chung in New York and John Kruzel in Washington; Editing by Will Dunham)