WASHINGTON - A Dutch ham radio operator has been able to learn about a psychological US special forces operation undertaken as part of the international military campaign designed to establish a no-fly zone over Libya.

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Listening to his radio, the ham operator in the Netherlands was able to monitor radio exchanges between civilian and military flights in the region and make his findings public on Twitter.

Hunched over his radio, he listens in on unencrypted exchanges between military aircraft and their air traffic control centers.

The messages contain information about the location of the planes, which is necessary to avoid collisions between military and civilian aircraft.

On Sunday, the radio operator posted a message on Twitter. The cryptic text of the message refers to an EC-130J aircraft, a modified version of the US Air Force's Hercules plane, whose registration number is 00-1934 and whose code name is "Steel 74".

The aircraft beams high-frequency messages on Libya as part of Operation "Odyssey Dawn", the international military campaign against the forces of Libyan leader Muammar Gadhafi.

The plane, belonging to US special forces, is used for propaganda and psychological warfare. It flies at high altitudes and broadcasts messages to influence the behavior of enemy troops or the population at large.

Asked about these operations, a senior Pentagon official confirmed that a "specialized aircraft" had been used by coalition forces.

"We've put up one of our specialized aircraft of that nature and I'm not ready, I'm not able to talk about the messages," Vice-Admiral Bill Gortney told reporters.

But one of the messages broadcast by the plane has been recorded by the Dutch ham radio operator and posted on the Internet.

Speaking over background noise, a man tries to deter Libyan vessels from going out to sea after coalition navy ships established a naval blockade.

"Libyan ships or vessels do not leave port," the message says. "The Gadhafi regime forces are violating a United Nations resolution ordering the end to the hostilities in your country."

Agence France-Presse