International sanctions and the effects of Libya’s civil war have disrupted normal supplies of fuel to parts of the country under Qaddafi’s control, but huge volumes of gasoline are instead being smuggled across the Libyan-Tunisian border.

“The armed forces are now conducting checks at fuel stations in the south of Tunisia, (in places) such as Tataouine and Ben Gardane and Remada, so that neither Tunisians nor Libyans can fill up with large quantities,” defense ministry official Mokhtar Ben Nasr told a news conference.

“These checks are aimed at preventing the smuggling of diesel and gasoline to Libya,” he said.

Tunisian police said on Wednesday they had seized five container trucks full of contraband fuel which was destined for areas of Libya under Qaddafi’s control.

Western governments trying to bring an end to Qaddafi’s 41-year rule believe that fuel supplies are crucial to his ability to hold onto power.

A NATO naval blockade and sanctions that prevent fuel traders from doing business with Libyan companies and individuals on a blacklist have made it extremely difficult for Qaddafi’s administration to bring in fuel by legal means.

However, smuggling networks help make up the shortfall. Libyans buy black-market gasoline in Tunisia, much of which has been smuggled out of neighboring energy producer Algeria, and then carry it across the border into Libya.

Until now there has been little evidence of Tunisian authorities taking firm action against the illegal trade with Libya. Smugglers provide a livelihood for some communities in Tunisia and so they constitute a powerful interest group.

Any blanket crackdown on fuel smuggling is also likely to hurt the Libyan rebels fighting Qaddafi’s forces.

Rebels in the Western Mountains region near Tunisia — who are trying to advance on Tripoli — depend on fuel smuggled in through a desert border crossing which they control.