The eight-month-old pup is now happily back with his owners. Picture: Mary Nguyen/Instagram

The “hostage” situation began last week, when Mary Nguyen, of Minnesota, hired Pet Air Carrier, a private company unaffiliated with Delta, paying it $4000 ($US3000) to ship Bunny, her German Shepherd, to Central America, where her husband lives, the New York Post reports.

As part of the arrangement, Nguyen, 25, drove from Minneapolis, where she is a student, to Wisconsin to have the required paperwork endorsed, before sending the pup on his way on Wednesday last week.

Bunny the dog was held hostage by Delta Airlines due to a paperwork mix-up, according to his owner Mary Nguyen. Picture: Mary Nguyen/InstagramSource:Instagram

But when Nguyen’s hubby tried to get Bunny out of cargo at La Aurora International Airport in Guatemala City, Delta baulked, saying the necessary paperwork to take the animal to a new country had been left back in the US, Marketwatch reported.

Adding insult to injury, Nguyen claimed Delta agents demanded an extra $3000 to free the pup, the site reported.

“They have all the documents they need on their scratch pad to release her but refuse to do so without the hard copy that they lost [but tracked down],” a distraught Nguyen told CBS.

“The document has been in their possession the whole [time] since I’ve surrendered my dog over.”

It took about 33 hours to get Bunny back, according to Mary Nguyen. Picture: Mary Nguyen/InstagramSource:Instagram

Nguyen told the site it took 33 hours of ‘dogged’ determination — and plenty of phone calls — to get Bunny sprung.

That happened late on Friday, after the paperwork was finally located and dispatched to Guatemala.

Most countries require specific vaccinations and a Certificate of Veterinary Inspection before an animal is allowed to enter from abroad.

Bunny, who weighs 28 kilograms, was an extra difficult case because of her size, Nguyen said. She needed an large crate, which is only allowed on certain aircraft. United Air Lines had previously rejected the dog before she was approved to fly on Delta.

The eight-month-old pup is now happily back with his owners. Picture: Mary Nguyen/InstagramSource:Instagram

Delta has had problems transporting pets in the past, with five animal deaths and five injuries in 2016, the second-highest rate of animal death and injury among the top seven US airlines.

United was ranked at number two, with nine deaths and 14 injuries.

Earlier this year, one of the world’s biggest rabbits died in cargo on a United Airlines flight.

A Delta spokesperson told CBS News that the airline would refund the shipment cost.

Once the drama was behind them, the owners took to Instagram to update their pup’s page, saying: “THANK YOU EVERYONE! Bunny has been released from @delta and we’re just waiting to be given the okay to be able to take her home now. Bunny’s got several open wounds on her, we will be taking her to a vet the minute we can.”

This article originally appeared on the New York Post and was republished with permission.