A Croatia fisherman found himself in a face-off with the US Navy after accidentally hauling a mysterious device out of the ocean.

Darko Bigava was fishing in the Elaphiti Islands, off the southern coast of Croatia, earlier this week when he pulled the object - comprised of a large orange box with metal fixtures at either end - aboard his vessel, the Marian II.

Bigava posted images of the device to social media in an attempt to identify the object, and a short time later was called on his cell phone by the US Navy demanding it back.

Darko Bigava, a fisherman from Croatia, was left mystified when he hauled a large orange box with some kind of sensor array attached to it out of the ocean earlier this week

He was fishing in the waters off the Elaphiti Islands when the object became entangled in his nets, which he claimed caused $3,000 in damage

The fisherman said he accidentally hooked the device while fishing at a depth of some 500ft near the island of Mljet.

The object is large - measuring some 1.3m square - and weights in excess of 220lbs (100kg). There was a smaller box attached to the first measuring about 15ins square.

Bigava first began trying to identify the object so that he could ask the owner for $3,000 to repair the nets that it broke when it became entangled.

He published the images online and contacted local newspaper Morski, and the story began circulating.

The box and an attache buoy contained almost no information on who might own it, except for a DHL shipping label attached to the side.

When reporters from Morski traced the parcel, they found that it had originate from NASA's Stennis Space Center in Mississippi.

It was shipped out of the US on November 20 last year, before making its way to Zagreb via Germany, where it arrived almost a week later.

After posting images of the box online in an attempt to identify the owner, Bigava said he was contacted by the US Navy demanding it back

Bigava said he refused to hand over the box until he was paid compensation, and after a tense series of conversations, the Croatian Coast Guard agreed to pay him

A reader also contacted Morski to report that US Navy research vessel Bruce C.Heezen had been in the same area the day prior, tracking back and forth over a stretch of water near Mljet island.

A short time later, Bigava said he was contacted on his ship's radio by the US Navy and demanded the device back.

Bigava said he refused until he was paid compensation for his damaged nets, prompting a series of back and forth messages that ended with the Navy calling directly to his cell phone.

Eventually the Croatia Coast Guard agreed to pay the damages, which they said would be recouped from the US Navy.

With the payment agreed, Bigava said he pulled up alongside the Bruce Heezen and threw the device overboard, before a dinghy picked it up and dragged it away.

The Heezen then set sail out of Croatian waters and towards Italy.

Bigava eventually handed the device over to research ship USS Bruce Heezen, which had been conducting maneuvers in the area just a day before, but says nobody will tell him what it was for or how it got there

As for what the device was, the orange object seems to be a weight with a sonar transponder attached to one end, and some kind of receiver attached to the other.

Such devices, known as HIPAP systems, are typically used for underwater communication and geolocation that is more accurate than traditional GPS.

However, the US Navy and Croatian Ministry of Defense refused to say exactly what this probe was being used for, or how it came to be caught in Bigava's nets.

In a statement, the MoD said: 'The Ministry of the Sea, Transport and Infrastructure has granted approval for the testing of marine research equipment and devices to the Navy research vessel Bruce C. Heezen, United States of America.

'The permit was issued in accordance with the provisions of the Maritime Code.'

Croatia and the US are allies, and are both members of NATO.