An investigation into the months-long intentional jamming of mobile satellite communications provided by Thuraya Satellite Telecommunications of Abu Dhabi concluded that the jamming came from Libya, one of Thuraya's shareholders, according to officials familiar with the episode.

In perhaps one of the most persistent jamming events ever recorded in the commercial satellite sector, Libyan nationals operating from three widely separated locations inside Libya--at least one of them a restricted military site--compromised the L-band communications signals from Thuraya for more than six months in 2006, officials said.

The jamming dealt a blow to Thuraya's 2006 revenues at a time when the company is trying to expand into Asia and complete the launch of its third satellite.

Officials said the jamming ceased only in late August 2006 after a diplomatic initiative made by the government of the United Arab Emirates to the government of Libya.

"Once the diplomatic channel was employed the problem was solved in a very short time," one official said. "Those doing the jamming were apparently concerned that smugglers carrying Marlboro cigarettes or other contraband from Chad or Niger into Libya were using Thuraya satellite phones. They wanted to disrupt their operations and thought this was a way to do it. I don't know whether they even realized the effect this was having on the Thuraya signal way beyond the borders of Libya."Thuraya officials have declined to comment on the problem beyond saying they relied in part on technical assistance from the Thuraya system's prime contractor, Boeing Satellite Systems International. Boeing officials also have declined to discuss the matter, referring questions to Thuraya. The Libyan embassy in Paris did not respond to requests for comment.

With the growth of satellite communications, globally signal jamming like piracy -- hijacking a frequency to replace the intended programming with the hijackers' message--has cropped up from time to time.

In Asia, both APT Satellite Holdings Ltd. and AsiaSat of Hong Kong have suffered the occasional TV-signal hijacking by groups believed to be in support of the Falun Gong dissident group in China.

In France, operators of the French Syracuse military telecommunications system say their satellites' signals in the Middle East have been subject to attempted jamming.

But in these cases the signals were compromised for only short periods or overcome by the satellites' onboard anti-jam systems in the case of the French Syracuse.

The head of one satellite-fleet operator said that in Asia in particular, his company has purposely offered narrow beams for certain markets to make it more difficult to invade the signal.

Several commercial satellite-fleet operators have said they are considering the addition of nulling antennas or other onboard gear to provide at least some protection to their satellite signals. But the cost of the added hardware remains an issue.

Industry officials said that once a signal is interrupted, it can take time to determine whether the interference is intentional or the result of misuse of a ground-based antenna by a novice operator.

This is what happened with Thuraya. Industry officials said that because of Thuraya's operations in the Middle East, and because Thuraya's owners include government-owned telecommunications operations from most Arab and Muslim governments in the region, the jamming was immediately assumed to be of U.S. or Israeli origin.

But as the weeks passed and the jamming did not cease or change characteristics, Thuraya was forced to maneuver its large satellite, located at 44 degrees east in geostationary orbit, to try to isolate the location.

"What you can do is turn the satellite slightly to see whether it changes the strength of the jamming signal," said one official. "As you perform the maneuver, you watch to see when the signal increases or decreases and this allows you to begin to determine the geographic location of the problem."

Officials said that once this was done, Thuraya deployed representatives to visit the areas where the jamming antennas were thought to be, and found that at least one of them was a Libyan military installation. "They were denied access to the site and told to turn around," one industry official said. "It was later determined that there were three sites performing the jamming operations, not just a couple of guys acting on their own. Having a shareholder do this was certainly not what we expected."