Royal Dutch Shell will revisit one of the darkest periods of its history tomorrow as a potentially groundbreaking court case opens in New York.

The oil giant stands accused of complicity in the 1995 execution of Ken Saro-Wiwa, a Nigerian environmental activist.

The world's boardrooms are watching the case, which is seen as a test of whether transnational companies owned or operating in the US can be held responsible for human rights abuses committed abroad.

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A collection of cases brought by torture victims in the oil-rich Niger Delta and by relatives of those killed has been brought together under the umbrella of Wiwa v Shell.

The plaintiffs include Ken Saro-Wiwa's son, Ken Wiwa Jnr, and his brother, Owens Wiwa.

For Shell, which denies any involvement in the environmentalist's killing, ordered by the government of Sani Abacha, the case represents an unwelcome public hearing of grievances that the company has spent time and money trying to make people forget.

Mr Saro-Wiwa was hanged in November 1995 after being convicted by a military tribunal in which he was denied proper legal representation or appeal. Shell subsequently faced a storm of protest and Nigeria was suspended from the Commonwealth. The then British prime minister John Major called the execution "judicial murder".

Tomorrow's proceedings will see the Dutch-based energy giant charged with collaborating with Nigerian authorities in the execution of Mr Saro-Wiwa and eight other members of his ethnic Ogoni group on "trumped-up charges". Shell has vigorously denied any involvement and says it appealed to the Abacha government for clemency on Mr Saro-Wiwa's part.

The suit also alleges that the company consistently conspired with military authorities to violently put down peaceful protests by the Ogoni people, hundreds of thousands of whom Mr Saro-Wiwa had helped to mobilise.

"I have always maintained that Shell was complicit in the conspiracy to silence my father along with thousands of other Ogonis," said his eldest son, Ken Wiwa Jnr.

Nigeria's oil industry has long been the most glaring example of what is called Africa's "resource curse".

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While Nigeria is Africa's largest oil producer, the peoples of the river delta where the crude is extracted have seen their homelands turned into a wasteland. The millions of dollars of oil revenue accrued every day have done nothing for the 70 per cent of Nigerians who live on less than $1 a day.

In the Niger Delta, farmlands and fish stocks have been destroyed amid environmental degradation brought on by oil spills, deforestation and the notorious practice of gas flaring, which continues despite being banned.

Ken Saro-Wiwa, an accomplished writer and businessman, had warned that Shell's actions in Nigeria would return to haunt them: "I and my colleagues are not the only ones on trial ... There is no doubt in my mind that the ecological war that the company has waged in the Delta will be called into question sooner than later and the crimes of that war duly punished."

The campaigner's death proved to be a turning point in the Delta and many of his darker predictions have since been borne out.

Oil production in Nigeria is running at half its capacity, the Petroleum Minister Odein Ajumogobia said last week. And the Niger Delta has been transformed into a war zone. The peaceful protests that peaked in 1993 with an estimated 300,000 Ogonis marching against Shell demanding compensation and an end to environmental destruction have been succeeded by armed militias in open revolt.

The demonstrations and sit-ins have given way to kidnappings, bombings, sabotage and armed assaults on oil rigs, pumping stations and multinational targets. The region is overrun with corrupt authorities orchestrating pirate gangs and wholesale oil theft.

As the preliminary hearings begin in New York tomorrow, hundreds of people in the Niger Delta are feared to have been killed in the crossfire during a counter-insurgency which the Nigerian government launched this month.

A joint task force carried out sea and air attacks against targets in the Delta and ground troops were sent in to flush out militants. Amnesty International condemned the operation.

The main militant group in the region is now the Movement for Emancipation of the Niger Delta, and unlike Mr Saro-Wiwa's Movement for the Survival of the Ogoni People, its tactics are avowedly violent.

The violence has affected all oil companies but analysts say that Shell's onshore fields have been the worst affected. The oil industry was judged to have fed the violence in the Delta, according to a report that Shell commissioned five years ago.

Shell has been active since 1958 in the Delta, which contains most of Nigeria's energy reserves, estimated at 36 billion barrels of oil and 187 trillion cubic feet of gas.

The plaintiffs in the case allege that, although the Nigerian government tortured and executed the claimants and their relatives, "these abuses were instigated, orchestrated, planned, and facilitated by Shell Nigeria" and that the company "provided money, weapons, and logistical support to the Nigerian military, participated in the fabrication of murder charges, and bribed witnesses to give testimony."

In a statement, Shell said: "Shell in no way encouraged or advocated any act of violence against [the claimants] or their fellow Ogonis. We believe that the evidence will show clearly that Shell was not responsible for these tragic events."

Ethnic groups in the Delta have wanted greater autonomy since before independence from Britain in 1960. The Ogoni campaign was built on perceptions among ethnic minorities that they were being cheated out of oil revenue by a corrupt government dominated by Nigeria's larger ethnic groups.