Rebels manufacturing massive quantities of drugs to sell for missiles and guns as they plan fight against junta

Elections promised for Burma this year have sparked an explosion in drug trafficking into Thailand, as rebel armies, fearful of a final, pre-poll crackdown by the ruling junta, trade heroin and amphetamines for guns.

For decades rebel armies, most notably the Wa State Army, have financed their fight against the oppressive Burma junta by running drugs over the border, from where they are trafficked all over the world.

A decade ago the Golden Triangle between Thailand, Burma and Laos supplied half the world's heroin. Afghanistan now produces more, but drug barons in Burma have turned to manufacturing massive quantities of amphetamines and methamphetamines – which can be produced cheaply in small, hidden laboratories, without the need for acres of exposed land.

Now Burma's illicit drug trade and the country's flawed electoral process appear set to collide. The Burmese junta has promised elections sometime this year, probably in October, though few in the international community expect them to be free or fair. The ruling generals have vowed to bring the rebel armies under their command, and turn them into border guard forces, before the polls are held.

With the deadline for the Wa to come under central government control gone, its leaders have become increasingly worried about being attacked by government troops. Colonel Peeranate Gatetem, head of the Thai army's anti-drug Pha Muang task force, said the number of drug runs had increased exponentially in recent months, as a desperate Wa – outnumbered and outgunned by the junta's troops – prepares to fight.

"This year will be the biggest for amphetamines," Peeranate said. "In all of last year we intercepted 1.2m pills. This year, in just six months, already we have seized 5m." He added that they were uncovering what they believe to be only a tiny fraction of what is being brought across the border, by most estimates between 1% and 2%.

"The amphetamine trade is huge now, we think it will be around 300m to 400m pills this year. But it is hard to know."

Sources from within Burma say the drug laboratories are working around the clock, with more under construction. In February, 15 smugglers were intercepted carrying 1.2m pills between them, and there have been reports of up to 30 Wa soldiers, in full uniform, marching through the forests fully laden.

The UN's Office on Drugs and Crime has also registered a rise in drug trafficking. "Minority groups that feel under threat from the central government are using drug trafficking to sustain themselves and keep control of their territories," Gary Lewis, a UN representative, said.

With the money it is making, Peeranate added, the Wa was arming with surface-to-air missiles bought from China, and AK-47 assault rifles. "They are preparing for war.

" The Burmese government wants the Wa to disarm, come under government control and become a border guard force. But the Wa will not ever agree to do that, so they are preparing for the government troops to move in on them.

"They are getting ready to fight. They are selling more and more drugs so they can buy weapons to fight the government."

The Guardian spoke to Wa soldiers just over the border, in Burma, about halfway between the Thai army border camp and Wa camp. "Burmese Army bad. They come shoot, shoot," one soldier said through an interpreter, mimicking machine gun fire.

The Wa will not participate in the election, he added, because it refuses to co-operate with the junta it says is illegitimate and brutal. "We protect our territory. We fight for [our] people."

TheWa refuse to discuss drugs, but he added: "Our life here is hard … we always need to make money some way, any way to feed our people. We need to survive."

In Thailand a former Wa drug runner, who now works undercover for the Thai army gathering intelligence on shipments, said: "The Wa are very worried, they think junta's soldiers are coming soon … the soldiers are afraid. They sell the drugs to buy many, many guns, so they can fight.

"The Wa fighters will be ready, and they will fight."