The federal government dealt another setback Friday to the Mashpee Wampanoag’s plans to build a casino in Taunton.

In a letter, Tara Sweeney, the assistant secretary for the Bureau of Indian Affairs, said that evidence does not show that the tribe meets certain federal requirements that would allow it to have a sovereign reservation to call its own. Tribes must have reservation status to open a casino.

Sweeney, in her letter, said she found in her review that the tribe was not “under federal jurisdiction” at the time of a landmark 1934 law, so it does not satisfy a requirement of a federal definition of “Indian.”

In a statement, tribal leaders referred to Friday’s determination as “an extremely disappointing decision,” vowing to continue their fight to retain their reservation and push for legislation to protect its land.

“We have been on this land for 12,000 years and we are not going anywhere,” said Cedric Cromwell, the Mashpee Wampanoag tribal council chairman, in a statement.

Cromwell said the decision underscored “the urgency of passing the Mashpee Wampanoag Tribe Reservation Reaffirmation Act immediately.” The act was filed in March. If passed, it would protect the reservation and put an end to the ongoing litigation, according to the tribe.

After the tribe’s federal acknowledgment in 2007, the tribe asked the US Department of Interior to acquire certain lands in trust for its benefit, including a parcel of about 170 acres in Mashpee and a 150-acre parcel in Taunton. The Bureau of Indian Affairs operates within the Department of Interior.

The Mashpee parcel was intended to be used for “tribal administrative purposes, tribal housing, and cultural purposes.”

The Taunton parcel was intended for a $1 billion casino. In 2015, the federal government issued a decision to acquire both parcels for the tribe on the grounds that the Mashpee Wampanoag had “maintained ties to an existing reservation since time immemorial,” according to a statement from the tribe, which has about 2,700 members.

The following year, Taunton property owners challenged that decision in federal court in Massachusetts. In that case, a judge sided with the Taunton property owners.

The future of the First Light Resort and Casino was stuck in a kind of limbo as the Department of Interior considered the tribe’s eligibility. Construction was suspended on the casino project, and the department indicated it intended to issue a decision in June 2017, but a decision was pushed back as parties “raised new and potentially important issues,” according to Sweeney’s Friday letter.

Sean P. Murphy and Milton J. Valencia of Globe staff contributed to this report.