(CNN) -- The Obama administration urged Qatar on Thursday to allow an American couple convicted of wrongdoing in the death of their adopted daughter to return to the United States.
A heightened State Department appeal comes after the family increased pressure on U.S. officials to do more to secure the release of Matthew and Grace Huang.
When their daughter, Gloria, died in January 2013, the couple was immediately arrested on charges they starved her to death.
The Huangs, who maintained their daughter suffered from an eating disorder, have denied any wrongdoing in connection with her death and are fighting the conviction.
Matthew Huang was employed in Doha by an international company working on construction projects for the 2022 World Cup.
Convicted at trial
After a lengthy trial, the Huangs were convicted of endangering the life of their child. They were sentenced in April to three years in prison.
The State Department has expressed concern about the fairness of the legal proceedings in the case and disappointment in the verdict.
It suggested that cultural misunderstandings were at the heart of the charges and that the evidence provided by the defense was not carefully considered.
Several U.S. officials have privately expressed confidence in the Huang's innocence, but have sought to exhaust all legal proceedings before seeking the Qatari government's direct intervention in the case.
After spending nearly a year in prison, the couple was released last November. They are prohibited from leaving Qatar during their appeal.
The case suggested racial overtones when questions were raised by the prosecutor and police about why the Huangs, who are Asian, adopted children from Africa.
State Department meeting
The Qatari prosecutor has sought to paint Grace and Matthew Huang as inhumane, alleging they bought their adopted daughter cheaply from her poverty-stricken parents in Africa and has since threatened to seek human trafficking charges.
The Huangs also have two adopted sons from Africa.
On Wednesday, Grace's brother, Daniel Chin, met with lawmakers and administration officials in Washington, urging them to make the Huang's case a greater priority.
He met with Assistant Secretary Anne Patterson and Undersecretary Wendy Sherman. Chin said he was assured more efforts would be made on behalf of his sister and her husband.
"Our family cannot afford to take people's word," Chin said. "We are starting to feel as if the State Department is abandoning Matt and Grace and our family."
Chin, who has given up his job in California to work on the case full time, does weekly skype chats with the Huangs and has traveled several times to Doha for their judicial proceedings, which the Qatari court continues to postpone.
"Justice deferred is justice denied," Chin said. "Enough is enough."
The case puts the United States in a difficult situation with a close ally it is working with on hot-button issues in the Middle East, including the civil war in Syria and the conflict in Gaza.
The Qatari government also helped the United States secure the release of Sgt. Bowe Bergdahl from Taliban captivity this year.
"We understand there are a lot of delicate things going on," Daniel said. "We understand Qatar is a big ally. But in all the discussions they are having with Qatar, why can't they bring more attention to the urgency of Matt and Grace's case? Seems obvious to me."
On Thursday, the State Department issued a statement saying that "assisting U.S. citizens in need overseas was among the department's highest priorities."
"The State Department will continue to engage Qatari officials at the highest levels. We seek the Qatari government's assistance in providing a fair and expeditious conclusion to the proceedings," spokeswoman Marie Harf said in a statement.
"We also urge the Qatari government to lift the current travel ban and allow Mr. and Mrs. Huang to return home to the United States to be reunited with their two sons and the rest of their family," she said.
Two sons back in U.S.
The couple's two sons were temporarily placed in a Qatari orphanage after the couple's arrest, but have since been back to the United States to live with Grace Huang's mother.
"It is heartbreaking to watch this family go through this," says Eric Volz, who heads up the firm David House that is assisting with the Huangs case. "Matt and Grace are fearful to go out in public. Being so far away and isolated and unable to be with their children is extremely stressful."
The case has garnered international attention and raised questions in the media about the prosecution, the overall fairness of the Qatari justice system.
"The Huangs case highlights the risks of Americans traveling to Qatar," says Richard Grenell, a spokesman for David House. "You could find yourself having to deal with an Islamic country's legal system with rules of evidence and procedures based on the whims of judges and their government controllers."