MAUNGDAW, Myanmar (Reuters) - The fence stretches as far as the eye can see, its concrete pillars carrying coils of barbed wire across the mountains and marshes of western Myanmar.
Beyond the fence, on the far bank of the Naf River, is a ragged horizon of mangroves: Bangladesh. There, say Myanmar officials, lurks the armed militant group the fence was partly designed to keep out.
The Rohingya Solidarity Organisation (RSO) takes its name from the mostly stateless Muslim minority living in Myanmar's troubled Rakhine State. Myanmar officials blame it for recent attacks here and believe it could foment more violence.
Most experts believe the RSO barely exists, with some saying it's being used to further oppress the Rohingya, who often live under apartheid-like conditions with little or no access to schools, jobs or healthcare.
Tens of thousands of Rohingya have fled the region by boat since 2012, after violent clashes with ethnic Rakhine Buddhists killed hundreds and displaced 140,000 people, mostly Rohingya.
The RSO is "essentially defunct as an armed organisation", said the International Crisis Group, a Brussels-based think tank, in an October report.
The RSO was set up in the early 1980s in the wake of a large-scale operation by the Myanmar military that drove about 200,000 Rohingya over the border into mainly Muslim Bangladesh.
Until the 1990s, a small number of militants trained at remote RSO bases in Bangladesh opposite Myanmar's Maungdaw district.
Myanmar officials blame the RSO for a series of deadly incursions in northern Rakhine State, including an attack on May 17 that killed four members of Myanmar's Border Guard Police.
Also jangling official nerves are threats against Myanmar by much more formidable militant groups.
In July, Islamic State leader Abu Bakr al-Baghdadi told followers to "take revenge" against Myanmar and other countries where Muslims were abused.
Then, in September, Al Qaeda leader Ayman al Zawahri announced the formation of an Indian branch that would "raise the flag of jihad" across the subcontinent, including Myanmar.
Within weeks, Myanmar's deputy home affairs minister, Brigadier General Kyaw Zan Myint, told parliament an extra 39 billion kyat ($38 million) was needed for Rakhine security, most of it earmarked to extend the fence.
If approved, this would constitute a doubling of the state's security budget of nearly 38 billion kyat.
The military began building the fence in 1995 and it is now 77 km (48 miles) long, said Kyi San, the head of Maungdaw Township. Its more remote stretches are routinely damaged by wild elephants or corroded by salt water.
For Buddhist officials like Kyi San, the RSO poses an existential threat.
Statewide, Rakhine Buddhists outnumber Rohingya Muslims by two to one. But only six percent of Maungdaw's 510,000 people are Rakhine or non-Muslim, Kyi San told Reuters during a rare visit to Maungdaw by a foreign reporter.
Kyi San feared RSO agents could radicalize this large Muslim community. "They take recruits back to Bangladesh for training," he said. "They have cells in all the villages."
The perceived threat extends beyond Rakhine State.
A roadside wanted poster near the capital Naypyitaw, in central Myanmar, features four RSO suspects, one of them an "explosives specialist".
The poster didn't say what they were wanted for, and Myanmar's Special Branch, when contacted by Reuters, declined to elaborate for reasons of "national security".
The Crisis Group report challenged the notion that the Rohingya were "ripe for radicalization". The Rohingya see Western governments, not the global jihadi movement, as key supporters, and most of their religious leaders don't preach violence, it said.
"Rohingya militancy is a myth," said Bertil Lintner, a journalist and author who has covered Myanmar for 30 years. The RSO once had a small camp in the Bangladeshi region of Ukhia, which borders Maungdaw district, but never had a presence in Myanmar, he told Reuters.
Many of those who trained at Ukhia were not Rohingya but youths from other Bangladeshi militant outfits, he said. The RSO faded as the Bangladesh government cracked down on Islamist groups. "Today, it hardly exists," he said.
Even though the RSO posed no real military threat, it provided a pretext to "squeeze and oppress Rohingya communities", said Matthew Smith of Fortify Rights, a Bangkok-based rights group.
"The authorities are conducting violent spot checks and accusing villagers of involvement with RSO, dragging men off and forcing others to flee," said Smith. "This has increased in recent months."
Maungdaw chief Kyi San denied the authorities were oppressing Muslims. "We have a duty to protect the weaker Rakhine community," he said.
Additional reporting by Min Zayar Oo and Jared Ferrie in Yangon; Editing by Dean Yates