The road from Harar runs for more than 600 miles east towards the border with Somalia, penetrating deep into the desiccated badlands of the Ogaden desert, the dusty heart of Ethiopia's war-torn Somali regional state.

Sparse scrub and thorn bush, brown termite mounds, and flocks of bony sheep edge up against the burning asphalt strip. Wandering camels are a hazard to traffic; but vehicles are few. Like the occasional herdsman, standing outside transportable mudul huts, they stare in mild surprise as white UN Land Cruisers race by.

The road's destination is Gode, via the regional capital of Jijiga, and the towns of Kebri Beyah, Degehabur and Kebri Dehar. But the part-finished two-lane road also blazes a figurative path, unwelcome to some, into the isolated and disputed fiefdoms of one of the world's most opaque, dangerous and misunderstood Muslim insurgencies.

This is the land that the self-styled separatists of the Ogaden National Liberation Front claim as their own. Exactly what the ethnic Somalis of the ONLF want - autonomy, independence, or the historic dream of a "greater Somalia" - is far from clear. What is certain is the federal government in Addis Ababa, dominated by Orthodox Christian Tigrayans and Amharans, is determined the Sunni insurgents' aims will not be achieved by violence.

Deep in these desert wastes lie the Somali state zones (provinces) of Degehabur, Fik and Qorahay. It is here, largely unseen and unreported, that the Ethiopian army, backed by rival sub-clans, has waged a violent nine-month-long campaign against factions of the Ogadeni clan, the backbone of the ONLF.

And it is here, in this wilderness of endless, shimmering horizons, vast untapped resources and suspected oil reserves that the UN says up to 4.5 million could soon face famine-like conditions, partly as a result of the conflict.

"There are strong reasons to believe such a catastrophe could occur in the next few months if all the necessary action to avert it is not taken," John Holmes, the UN undersecretary for humanitarian affairs, warned in December.

Federal and state officials dismiss such claims as wildly exaggerated, saying six of Somali state's nine zones, where the majority of the region's population lives, are peaceful. While conceding there may have been "a few problems" involving individual soldiers, ministers insist ONLF claims of ongoing atrocities committed by Ethiopian troops - claims supported by Human Rights Watch - lack foundation.

"The situation is very calm now. We have destroyed [the ONLF]," said Abdullahi Hassan, the Somali state president. Pointing to continuing strife in next-door Somalia, where Ethiopian and African Union troops support the western-backed Transitional Federal Government against hardline Islamists and warlords, he said the trouble was not homegrown.

"If there is a problem with your neighbour, the problem will touch you. For years Somalia has been harbouring international terrorists linked to al-Qaida and anti-peace elements," Abdullahi said. And much of the unrest was being orchestrated by Eritrea, Ethiopia's long-time enemy, he claimed.

Abdi Mohmmad Omer, Somali state security chief, said: "The war is no longer between the ONLF and the government, it is clan against clan, against some of the Ogadeni who are connected to al-Qaida."

Abdi also said the region had been "pacified". But he said about 200 civilians had been killed in clan fighting with the ONLF in the past two months. While declining to estimate how many had died since the conflict escalated last summer, he dismissed as absurd ONLF claims that a genocide was taking place.

Sulub Abdullahi Mohammad, an elder of the Jedwaq tribe, said his people, like the Wayteen and Balaad sub-clans, regularly confronted the ONLF militants who, he said, still posed a serious threat. He pointed to a recent bombing and shooting in Jijiga in which a traffic policeman and a bystander were killed. "The number of deaths is uncountable. The fighting has gone up and down in the past six months. But it is not over."

Trying to get people to describe what is happening is difficult. Much of the population comprises semi-nomadic pastoralists who tend to eschew foreign media. Down the Harar road, in the crowded, unpaved streets of Degehabur, a market town of 60,000, residents seem caught between concern over how the authorities might react and fear of insurgents. Few talk openly.

One woman, speaking tearfully inside her house, tells a female reporter she was raped by a soldier. But she insists her name not be publicised. She can provide no "evidence". She has, she says, much shame - and no hope of justice.

Nur Arab, Degehabur's administrator, does not pretend problems do not exist. He says there has been "a big change for the better" since the UN and NGOs returned in strength recently, having been largely excluded during the army crackdown. Most of the town's residents have received food aid, he said.

"The ONLF has no base here. They are not organised. But sometimes they come into the streets and they disturb the people," Nur said. "They are in groups of 15 or 20 maximum. They are often very young. They demand money and help from the people. If somebody does not give, they will kill them. They appear, then they disappear."

Following earlier warnings, the UN says relief work is proceeding relatively unimpeded. Nineteen NGOs have returned to the area. Others may follow.

An extra $600,000 (£300,000) has been allocated to the World Food Programme to help Ethiopia deliver supplies. But "the humanitarian situation within the military operational area continues to be of concern," the UN Office for the Coordination of Humanitarian Affairs said. It suggested a bigger, natural problem was that the rains had failed in several zones and crop output was declining. The UN launched a $4m drought appeal this month.

Even if the situation has eased, there is no end in sight to the conflict. The ONLF has again accused Addis Ababa of killing and starving thousands. It claimed the UN had been duped into collaborating. The government was using aid as a political tool. "Ethiopia is doing all [this] to suppress the people's resistance against tyranny and violation of their human rights." The insurgency might intensify, it warned.

As if they did not know it, for the troubled clans of the Somali regional state a long hard road awaits. In the Ogaden, it has always been thus.