Story highlights "We are deeply concerned about new delays that have prevented their departure," says Kerry

New arrest warrant issued for American couple, Doha News reports

The development comes after a judge voided their conviction in their daughter's death

Prosecutors accused them of starving the girl to death

An appeals judge in Qatar on Sunday cleared American couple Matthew and Grace Huang of starving their adopted daughter to death in 2013, in a case that drew global attention to the Middle Eastern nation's justice system.

However, the couple were blocked from leaving Qatar on Sunday by immigration officials at Hamad International Airport, who confiscated their passports, according to the Doha News agency, which cited a family spokesman Eric Volz.

A new warrant had been issued for their arrest on unknown charges, the agency cited Volz as saying. The couple remained at the airport Sunday night with the U.S. Ambassador to Qatar, Dana Shell Smith, Doha News reported.

Earlier, Matthew Huang issued a statement thanking the Qatari judge for his decision.

Matthew and Grace Huang speak to reporters outside the entrance of the Court of First Instance before their trial in Doha, March 27, 2014.

"This has been an emotional trial for me and my family," Matthew Huang said in a statement. "Grace and I want to go home and be reunited with our sons. We have not been able to grieve our daughter's death, but we want to thank the judge for today's decision."

The Huangs -- who were living in Qatar while Matthew Huang worked for a international company working on construction projects for the 2022 World Cup -- were arrested in January 2013 when their 8-year-old daughter Gloria died.

They were charged with starving her to death, convicted in March and sentenced to three years in prison.

The Qatari prosecutor sought to paint Grace and Matthew Huang as inhumane -- alleging they bought their adopted daughter cheaply from her poverty-stricken parents in Africa -- and had threatened to seek human trafficking charges.

The couple spent nearly a year in prison before being freed in November 2013 pending their appeal.

In explaining his decision to overturn the conviction, Judge Abdulrahman al-Sharafi cited weaknesses in forensic reports and said the trial judge failed to properly consider testimony from witnesses who said Gloria wasn't deprived.

A report by pathologists hired by the defense, obtained by CNN, stated they found no evidence tissue samples were taken from Gloria's body after her death, despite the fact Qatari investigators submitted an autopsy report.

Advocates for the Huangs suggested the lab report was fabricated and said their request with the Qatari judiciary for a formal investigation went unanswered.

Criticism of Qatari justice

The case against the Huangs shined a light on the Qatari justice system and drew complaints from the United States.

Qatar is a key ally in the U.S.-led coalition against the terror group ISIS and host to many countries' forces involved in airstrikes. The Qatari government also helped the United States secure the release of Sgt. Bowe Bergdahl from Taliban captivity this year.

Despite the close ties, the State Department expressed concern. Officials requested in October that Qatar's government lift the Huangs' travel ban, allowing them to return to the United States.

"The 22 long months of court proceedings following their daughter's tragic death have compounded the tragedy for the Huang family, and it is time now, as the Appeals Court stated, to let the Huangs return home," U.S. Secretary of State John Kerry said in a statement.

"We are deeply concerned about new delays that have prevented their departure," he said.

A United Nations special rapporteur investigating the justice system in Qatar also called attention to the Huangs' case and urged the government to release them and send them home.

Fighting family

After the couple's arrest, their two sons, also adopted from Africa, were temporarily placed in a Qatari orphanage. They have since been sent back to the United States to live with Grace Huang's mother.

The entire family chipped in during the prolonged separation. With Matthew Huang fired from his job, the couple are living on donations from family and friends.

Grace Huang's brother, Daniel Chin, gave up his job in California to work on the case full time. He was the nerve center of the family, raising money for expenses and defense costs and dealing with the Huangs' lawyers and advocates.

Their focus on their fate took away from time for them to grieve Gloria's loss.

"Everything has revolved around her case and our situation," Grace Huang said. "We haven't had a chance to really say goodbye and mourn. We just really want to be able to honor her place in our lives with our friends and family and that hasn't happened yet."