War on Kachin rebels has intensified but gone entirely unnoticed, with abuses overshadowed by drive for political reform

The villagers scattered as machine guns raked the darkness, fleeing from the Burmese troops into the thick of the jungle. When day came they crept from their hiding places to find each other.

Nu La could not see his wife until he followed the wail of their two-week-old baby. Her body lay close to her son, between two large rocks, slumped to the right. The slash wound that killed her ran all the way from one side of her chest to the other.

The mother of four was a casualty of a brutal six-month conflict between the Burmese government and ethnic minority rebels from Kachin, a state in northern Burma bordering China. This is a war that has killed and maimed countless civilians and caused 30,000, probably more, to flee, yet has gone almost entirely unnoticed, as the outside world chooses instead to focus on the possibility of a Burmese thaw and rapprochement with the generals. As Hillary Clinton visited the country last month – and as William Hague prepares for a rare official visit to Burma early in the new year, fighting has intensified in Kachin.

"There's so much focus on political reforms from the international perspective, but human rights abuses that are continuing are being ignored. It doesn't fit into the narrative," said Lynn Yoshikawa of Refugees International, who visited the region this month.

The government announced a ceasefire last week, but sources in Kachin areas said clashes continued. Among the allegations made by Kachin civilians interviewed by the Guardian along the Chinese-Burma border were:

•Burmese troops attacked villages without warning, injuring and killing civilians.

•Numerous civilians vanished in areas occupied by the military.

• Soldiers pillaged homes and forced villagers to carry away their plunder.

• Troops subjected men to brutal interrogations.

• Chemical agents were used around one village, possibly to push people out of the area.

Groups including Human Rights Watch, Physicians for Human Rights and Partners Relief and Development have also gathered numerous accounts of abuses. Organisations say that while the Kachin Independence Army (KIA) has also committed violations, government soldiers are responsible for the vast majority.

"Abuses have been extreme and have been a rallying point for people to back the Kachin Independence Organisation [political wing of the KIA], now more than ever. Support for the KIO is really at a peak," said Yoshikawa.

"Troops know they won't be held accountable for serious violations of the laws of war," said David Mathieson, Burma researcher for Human Rights Watch, noting that similar military behaviour had been documented around the country.

"It's like a set menu of abusive practices: forced labour, torture and the destruction of property and livelihoods."

The longrunning conflict is one of many between the Burmese state and ethnic groups which reignited two years ago as the government sought to extend its hold. Skirmishes between government troops and the KIA erupted into outright conflict this June, ending a 17-year ceasefire.

"The resumption of fighting in Kachin areas … is the most serious threat to peace in Myanmar," a recent International Crisis Group report warned.

"The KIO was the group that approached the ceasefire with probably the greatest strategic thought, and they went very far in co-operating with the military government's roadmap. The consequences of that ceasefire failing are grave."

No one has felt those consequences more acutely than Nu La and his family, who fled with fellow villagers as the Burmese army approached early this month.

Troops stumbled across them as they sheltered in a jungle camp overnight. When Nu La got up to see what was happening, soldiers fired four shots towards him and a mortar before shouting in Burmese and Kachin: "Don't flee!"

The families were too frightened to comply.

"It was like a battle. Then the machine guns came," Nu La said. "The shooting was for around 15 minutes. They shot and we fled … We were all afraid and ran in different directions."

He wept as he described finding his wife of 15 years the next morning. Beside him, their eight-year-old daughter dandled her baby brother in an imitation of motherhood.

Another neighbour was wounded by gunfire and two more are missing, Nu La said. One was holding her four-year-old daughter when she was shot in the leg.

"Her daughter said [the soldiers] injected medicine into the woman and took her away. I saw pieces of her clothes on the way. I don't know what happened to her," he added.

Map of Burma

Mathieson said many disappearances suggested forced labour or interrogation, and that there were concerns women had been abducted to be abused. The Kachin Women Association of Thailand has logged around 40 cases of alleged rape or sexual abuse by soldiers.Another civilian gave a detailed account of a November assault on settlements between KIA and Burmese military lines. Hkun Awng described a four-day attack, with the army firing what he believed were chemical agents into areas around their villages – possibly to force them further and further out of the territory.

"With the one that explodes on the ground the smoke is black and everything afterwards is black. It was like you had poured engine oil on the ground … The grass and leaves and bark were all completely black.

"With the other it explodes in the air. They shoot two [shells] together: one with white cloudy smoke and the other with brown smoke."

When villagers went to investigate, children and the elderly were immediately affected, he said, and others more gradually."The throat dries up. It feels like wanting to cough. You feel nauseous and want to vomit and your body weakens."

Experts said the nature of the substances was unclear. Anti-crop agents would usually take days or weeks to work. While CS gas makes some individuals nauseous, irritant effects usually predominate, said Alastair Hay, professor of environmental technology at Leeds University.

CS gas and other riot control agents can be used in civil disturbances but are forbidden in warfare under the 1997 Chemical Weapons Convention (CWC), which Burma has signed but not ratified. Professor Julian Robinson, an expert on chemical weapons at Sussex University, said allegations of Burmese use were "both numerous and – at least to my mind – unresolved".

There have been widespread claims of brutal interrogations and Zahkung Nu Nu, from a Kachin area of northern Shan state, said she witnessed a neighbour's torture in early September. The 18-year-old civilian was singled out by troops who halted her party of villagers as they fled.

"They poured water over him and then covered his head with a plastic bag so he was struggling to breathe. They did it for about 10 or 15 minutes, then pulled it off and beat him, then poured water and covered his head, again and again.

"They were asking questions like 'Are you KIA?' He said no, I'm a civilian. He said it again and again and they didn't believe him," she said.

The torture ended after two hours when a soldier who knew the man's parents intervened, she said.

Other villagers, whom she met on a surreptitious return to her home, told her they had been forced to act as porters – perhaps the fate of her husband, too; she has not seen him since their chaotic escape.

"They had to carry their belongings and the belongings of villagers. I went hoping to bring back my things, but when I arrived at my house, nothing was left," she added, describing how everything from cooking pots and rice to traditional clothes had vanished.

A headman from another area said that even before the ceasefire ended, troops had forced villagers to log trees and carry loads of bricks for their base, paying small sums or nothing at all.

He added that the fighting was much worse than in previous outbreaks. Troops were using mortars as well as guns and firing more often.

"They just used people to show them the way or forced them to be porters," he said.

"During the current fighting it's very different: when they see civilians, they know they are civilians, but they shoot and kill them."

His own son has been missing for more than three weeks, but no one dares to return to look for him.Some witnesses complained that troops seemed to assume all Kachin were KIA members or active supporters.

"In other cases it is clear they have simply gone into an area and shelled the village and watched people run away – and then quite often destroyed food and made the area uninhabitable. They create huge areas which are free fire zones and basically shoot on sight," said Mathieson.

"It is not necessarily to kill people but to drive them away, to deny support [for the KIA] and tie up their resources as people flee into their areas."

The Guardian has changed the names and withheld details of interviewees, because they fear retaliation.

Burmese authorities did not respond to questions. An official at the embassy in Beijing said that information on Kachin was available from state media and that the foreign ministry was busy preparing for a summit.

The government has signed deals with other ethnic groups in recent weeks and has met Kachin representatives for discussions, bringing hope for a resolution.

Aung Thaung, the minister of industry and head of the Union Level Peace-Making Group, said on Friday that the government wanted "everlasting peace" and hoped to sign agreements with all ethnic groups within three years.

Asked why troops had not followed the presidential order to withdraw from combat with the Kachin, he told Reuters there might be skirmishes due to problems communicating with troops in remote areas.

In another possible sign of progress Unicef and UNHCR officials last week were allowed to visit Majiayang, where many of the displaced Kachin have fled. The World Food Programme has been able to visit only government-controlled areas, but hopes it may now be able to extend its programme – at least until funding for Burma runs out, in February.

A Kachin volunteer said psychological issues were as acute as food shortages and health problems, with traumatised families further distressed by recent fighting. "People are crying in their mind," she said. When they hear gunshots, "they are frightened and want to escape again".

Ceasefire strains

The Burmese government has been in conflict with ethnic minorities such as the Kachin, Karen and Shan since independence in 1948. Longstanding ceasefires collapsed two years ago as it tried to bring their militias under national army control and while President Thein Sein promised this spring to make the issue a national priority, an upsurge in fighting followed.

In recent weeks authorities have reached ceasefires or deals with several groups. But the Kachin are particularly wary. The Kachin Independence Organisation – allied to the Kachin Independence Army – agreed to participate in the government's political roadmap in the 1990s and co-operated even when its proposals were ignored. Yet Kachin candidates were blocked from standing in 2010's elections and the government became increasingly hostile, declaring the ceasefire null and void.

Kachin grievances have been exacerbated by government-backed projects that displaced inhabitants and brought them little benefit: "With the [Myitsone] dam, mining, other infrastructure – there's a sense of being politically marginalised and exploited at the same time," said David Mathieson of Human Rights Watch.

The government surprised many by axing the massive Chinese hydropower project in September, but the International Crisis Group warned that did not solve the underlying problems. A recent report praised the president's bold peace initiative but warned that the most difficult deal to reach might well be with the KIO.

• The picture caption on this article was corrected on 19 December 2011 because the original identified the Kachin fighter as holding "a rocket launcher". This was based on the caption material supplied. The weapon is a type of assault rifle.