American couple Grace, right, and Matthew Huang walk to their gate with U.S. Ambassador to Qatar, Dana Shell Smith, center, at the Hamad International Airport in Doha, Qatar, Sunday, Nov. 30, 2014, before they were barred from boarding the flight. (Osama Faisal/AP)

A California couple who spent nearly year in a Qatar jail on child-endangerment charges remained in limbo Sunday after Qatari officials blocked their departure from the country — hours after their acquittal in the 2013 death of their adopted daughter.

Matthew and Grace Huang of Los Angeles remained stranded at Doha’s Hamad International Airport well into the evening as U.S. officials stepped up diplomatic and public pressure on Qatar’s rulers to allow the couple to fly home. Secretary of State John F. Kerry phoned Foreign Minister Khalid bin Mohammed al-Attiya late Sunday urging Qatar to “permit their return without delay.”

“It is time now, as the appeals court stated, to let the Huangs return home,” Kerry said in a statement. “We are deeply concerned about new delays that have prevented their departure.”

The snag came hours after an appeals court judge tossed out a guilty verdict and three-year prison term for the Huangs, who were arrested in January 2013 in connection with the death of Gloria, an 8-year-old Ghanaian girl they had adopted. A Qatari prosecutor initially brought murder charges against the couple in a highly unusual case that garnered international attention as well as allegations of cultural bias on the part of Qatari officials.

Kerry, weighing in forcefully on the legal substance of the case, said the “thoroughly documented findings of the court clearly establish” the Huangs’ innocence.

“The 22 long months of court proceedings following their daughter’s tragic death have compounded the tragedy for the Huang family,” Kerry said.

The reason for the couple’s further detention was not immediately clear.

“Currently, Matt and Grace are at the airport trying to get out of the country after being declared innocent by a Qatari judge,” said Richard Grenell, a spokesman for the Huangs. “We are all focused on getting the U.S. and Qatar authorities to work through this mess — they need to be allowed to leave.”

Attempts to reach the Qatari Embassy for comment were unsuccessful.

The acquittal by appellate judge Abdul Rahman al-Sharafi had appeared to bring a long-sought resolution to the Huangs’ nearly two-year legal ordeal. After the decision was announced, the Huangs made plans to immediately leave Qatar to be reunited with their two adopted sons, whom they have not seen for months.

“This has been an emotional trial for me and my family,” Matthew Huang said in a statement read shortly after the court decision was announced. “Grace and I want to go home and be reunited with our sons. We have been unable to grieve our daughter’s death. But we want to thank the judge for today’s decision.”

The Huangs moved to Doha with their three children in 2012 after Matthew Huang accepted an engineering job related to Qatar’s preparations to host the World Cup in 2022. But while there, Gloria suffered from health problems that the family says stemmed from a chronic eating disorder. At the time of her adoption, the girl suffered from giardia, a parasitic condition that sometimes results in a long-term impairment of the body’s ability to absorb nutrients from food.

After refusing to eat for several days, the girl collapsed at home on Jan. 14, 2013, and died at a Doha hospital of what doctors said was cardiac arrest. Qatari officials suspected foul play and accused the Huangs of deliberately depriving their daughter of food and water. A prosecutor initially sought the death penalty and briefly put the couple’s two boys in an orphanage.

The State Department has repeatedly expressed concern over the case, and a number of advocacy groups, including the California Innocence Project , have championed the cause. The project’s legal experts provided pro bono counsel for the family, contending that the charges against the couple were “rooted in transparently racial and cultural prejudice” by Qatari law enforcement officials, the group said in a statement. The Huangs are of Asian descent, and their three adopted children were born in Africa.