HARTFORD, Conn. — Ten people suing former Mexican President Ernesto Zedillo for $50 million over a 1997 massacre in a Mexican village are taking their case to a U.S. appeals court after a judge in Connecticut dismissed their lawsuit, their lawyer said Monday.

The unnamed plaintiffs say they are survivors of the killings of 45 people in Acteal in the southern state of Chiapas. They sued Zedillo in 2011, alleging he bore some responsibility for the massacre and covered it up.

But a legal doctrine giving former heads of state immunity from lawsuits applies to Zedillo, U.S. District Judge Michael Shea in Hartford ruled Thursday, and he dismissed the case.

Zedillo denies the allegations, and the U.S. State Department backed his immunity claim. But the State Department based its immunity recommendation on an illegal and unauthorized letter by the Mexican ambassador, said Roger Kobert, a Miami-based attorney for the plaintiffs. He said he will appeal Shea's dismissal to the 2nd U.S. Circuit Court of Appeals in Manhattan.

The lawsuit was filed in Connecticut because Zedillo, president of Mexico from 1994 to 2000, is now an international studies professor at Yale University in New Haven.

Zedillo has called the allegations slanderous and groundless. Any appeal of Shea's ruling would be futile, his lawyer, Jonathan Freiman, said Monday.

The massacre on Dec. 22, 1997, was the worst instance of violence during a conflict that began when the Zapatista movement staged a brief armed uprising in early 1994 to demand more rights for Indians in the southern state of Chiapas. During a prayer meeting in Acteal, paramilitaries with alleged government ties attacked Roman Catholic activists who sympathized with the rebels. The assailants killed 45 people over several hours, including children as young as 2 months old.

After the killings, Zedillo denounced them as criminal and urged government and human rights officials to investigate.

The plaintiffs' lawsuit alleges that Zedillo's administration ended peace talks with the Zapatistas and launched a plan to arm and train local militias to fight them. It also claims Zedillo was aware of the actions in Acteal, covered them up and broke international human rights laws under the Geneva Conventions as well as a host of other laws.

Last September, the Justice Department notified Shea that the State Department determined Zedillo was immune to the lawsuit and suggested Shea also find that immunity applied to Zedillo.

Kobert said the State Department's determination was based on a written request for immunity for Zedillo by the Mexican ambassador to the U.S. Kobert said the ambassador's letter to U.S. officials was declared void this year by a Mexican court, which ruled that the ambassador wasn't authorized to request immunity for Zedillo.

A Mexican appellate court later overturned that ruling, but Kobert said it was based on a technicality and not on the merits of whether the ambassador's letter was illegal.

"We're disappointed," Kobert said. "We were hopeful that Judge Shea would have given the State Department a chance to correct the decision (on Zedillo's immunity) in 2012 that was incorrect. We would like the State Department to look at it with a fresh set of eyes."