As the Sri Lankan Army closes in on the separatist LTTE rebel heartland, they are capturing the LTTE supply dumps, training areas, headquarters, medical facilities and weapons factories. This last item is common for successful rebellions. Making your own weapons is not that difficult. The main component is explosives and detonators, and these are smuggled from abroad in bulk. Both items are widely available on the international black market. But rather than just use it for bombs, rebels know that they can also build mortar shells and mines. The latter are banned by international treaty, but they are quite easy to manufacture. Metal working equipment, which is legal and easily obtainable, is used to construct the shells and mine bodies. Designs for both are widely available, even before the Internet came along.
These factories were widely used by guerilla movements during, and after, World War II. During the Vietnam war, such weapons factories were widely used, with the explosives often obtained from dud (unexploded) American bombs and shells. In Iraq, Islamic terrorists also obtained explosives from shells and bombs plundered from the many Iraqi Army weapons storage sites, left unguarded right after the fall of Saddam's government. Most of these explosives went to build roadside bombs, which employed a wide range of wireless devices for detonators. In Gaza, Palestinian terrorists use metal working tools and common chemicals to manufacture propellant and explosives for their Kassam rockets. Note that rocket propellant is basically slow burning explosives. Once you know how to mix the chemicals, you can control the burn rate of the explosives.
It's become an axiom of counter-terror operations to hunt down the weapons workshops and, in particular, those with the technical skills to mix the chemicals and build the devices. Israel used this technique very successfully to shut down the Palestinian terrorist bombing campaign inside Israel. In Iraq, U.S. and Iraqi forces applied the same tactics to destroy the terrorist bombing campaign there. But in Sri Lanka, the LTTE had territory under its exclusive control for over a decade, and were able to build camouflaged, or underground, weapons factories.
Even though there is increased effort to destroy these improvised factories, terrorists and rebels have gone to greater lengths to protect their weapons manufacturing facilities. Some are made mobile, others are put in underground bunkers and guarded carefully. Thus, even for "irregular" wars, logistics and manufacturing are key components of the conflict. Take out the enemy weapons production capability, and you take a large step towards defeating the foe.