A young North Texas couple vacationing in Fiji died from an unidentified illness, authorities said Tuesday.

The couple arrived in Fiji on May 22 and were taken to a hospital after they became ill, according to Fiji's Ministry of Health and Medical Services. It said in a statement their conditions worsened despite medical care and they died within a few days of each other.

The ministry said it was working with police forensics, the World Health Organization and the U.S. Centers for Disease Control and Prevention to try to determine what caused the deaths. The ministry said it had put in place public health measures, although didn't immediately identify what those were.

The couple was identified as Michelle and David Paul, a representative of the U.S. State Department told NBC News, adding that officials are "monitoring local authorities' investigation into the cause of death."

The pair are from Fort Worth, Texas.

Michelle Paul's father, Marc Calanog, said that the pair were treated and released from a local hospital for diarrhea and vomiting, but he still doesn't know the cause of death either.

"That's very hard for me," he told NBC News.

Calanog said that he and his wife have been caring for the couple's young son since the couple dropped the boy off before their trip.

"I keep telling my wife we got to stay strong," Calanog said, because they have to care for the child.

Fiji is home to just over 900,000 people and is a popular tourist destination thanks to its warm climate, white sand beaches and coral reefs.