It's one of Myanmar's smallest ethnic insurgencies, just a few thousand fighters scattered between isolated villages in the mist-shrouded mountains of northern Shan state. But as President Thein Sein struggles to reach a nationwide peace agreement by the year's end, the Ta'ang National Liberation Army has turned into one of his biggest obstacles.

The rebels have so far refused to negotiate the terms of a ceasefire, citing the lack of discussion about their aspirations, such as greater control over natural resources for the half-million ethnic Ta'ang people. When they last agreed to hand over weapons in exchange for a "self-administered zone," nearly a decade ago, the insurgents say, they saw little or no real benefits for their people.

"In fact," said Main Aik Kyo, a rebel army spokesman, "things only got worse."

Soldiers and pro-government militias continued to harass local residents, he and others say. They also stepped up involvement in the illegal narcotics trade in the opium-growing region. The widespread availability of drugs has led to alarming addiction rates. One village head said half of all Ta'ang men are now hooked on drugs, some as young as 13.

Myanmar stunned the world by opening politically and economically in 2011 following elections that most rights groups say were neither free nor fair. Though the new president started steering the country from a half-century of dictatorship toward democracy, early much-lauded reforms have since either stalled or started rolling back.

That's upped the stakes of getting ceasefire deals with all 17 ethnic armies, one of Thein Sein's biggest pledges. Many ethnic armies have been fighting since the country gained independence from the British in 1948, and experts say continued civil unrest is slowing development in one of the region's poorest countries.

The TNLA, one of four rebel groups still holding out, claims to have 4,000 troops.

Though those estimates are believed to be inflated, a celebration last month in the isolated village of Mar Wong, nestled deep in the jungle-clad mountains, showed that support among villagers is as strong as ever.

Hundreds turned out, making long, treacherous journeys along steep, windy roads. Huddling beneath blankets to protect themselves from icy winds, they cheered as 650 troops goose-stepped with guns or while waving green and red flags.

"We have to keep fighting for our freedom, for our political rights," said Thar Phone Kyaw, the TNLA general secretary, adding no ceasefire agreement will be signed without assurances they will get the "federal union" promised to them by Myanmar's independence leader Gen. Aung San more than 60 years ago.

That would give them greater control over their natural resources, including a say in issues surrounding an oil pipeline to China that has displaced people and destroyed livelihoods. It would also allow them to control their own troops' movement and help end the spiraling scourge of drugs.

Ta'ang men and women in traditional attire applauded and took pictures with their smart phones as the rebels set fire to a huge haul of opium, heroin and methamphetamine tablets. Children and novice Buddhist monks covered their noses and mouths as the dark smoke rose from pile.

The rebels also displayed weapons and ammunition allegedly confiscated from Myanmar soldiers during recent confrontations.

Though the TNLA only started fighting again four years ago, the grievances of the Ta'ang date back to the early 1960s, when Gen. Ne Win seized power in a bloody coup, imposing policies that actively promoted the Bamar, or Burman, ethnic majority to position of power.

Ethnic groups, representing 40 percent of the population, found themselves victims of military abuses and discrimination in areas spanning from health and education to road construction and access to electricity.