WASHINGTON — The US Supreme Court began its new session on Monday by re-examining an explosive international case alleging that oil giant Shell was complicit in acts of torture by the Nigerian government.

Fresh from their pivotal decision in June to uphold President Barack Obama's health care overhaul, the nine Supreme Court justices took up a case with enormously important ramifications for international human rights.

The legal argument pivots on whether foreign plaintiffs have a right to file suit in American courts against US corporations accused of human rights violations, under an arcane 200-year-old statute.

In Kiobel v. Royal Dutch Petroleum, the oil giant is accused of being an accomplice to torture, extrajudicial executions and crimes against humanity by the Nigerian government between 1992 and 1995 in the Niger Delta region.

Shell is alleged have helped the former dictatorship arrest and torture 12 members of the Ogoni tribe, who had sought to peacefully disrupt oil development because of its health and environmental impacts.

Esther Kiobel, now a US citizen, brought her claims on behalf of her late husband, Barinem Kiobel, who was executed in a sham trial in which Shell is alleged to have played a key role.

Plaintiffs have invoked the Alien Tort Statute (ATS), which allows non-citizens to sue in US courts for violations of international law.

Human rights lawyers already use the obscure statute to seek damages in US courts from foreign governments involved in human rights abuses.

At issue now is whether multinational corporations, allegedly complicit in such overseas abuses, are also liable.

Justices indicated in February that the statute doesn't permit suits against corporations but decided to re-examine the wider question of whether the statute can apply beyond US borders.

"ATS clearly covers those violations," argued Carey D'Avino, one of the plaintiffs' attorneys.

The 1789 statute was barely used for two centuries before being resurrected in the 1970s by human rights activists to pursue international lawsuits.

This case is being closely watched as it has implications for several other pending actions, including a group of Indonesian villagers who accuse oil giant Exxon Mobil's security forces of murder and torture.

Attorneys for Shell argue that the oil giant cannot be held legally responsible in the United States for offenses allegedly committed far from American shores.

"This case has nothing to do with the US," said Shell attorney Kathleen Sullivan, adding that the petitioners were seeking legal redress "against an Anglo-Dutch corporation for something that happened entirely in Nigeria."

But Paul Hoffman, lawyer for the Nigerians, told the court that the plaintiffs, who have been granted asylum in the United States, sued here because this was their "adopted homeland."

The Committee for Constitutional Rights, a non-profit group, said it was worried that a negative ruling would damage the ability of the United States to take the lead on international human rights issues.

"The ATS has been a cornerstone of US human rights litigation for over three decades, providing victims of grave human rights abuses justice that they could not get elsewhere," the group said.

A decision is not expected until next year.

During its new nine-month session, which runs through June 2013, the Supreme Court will also consider a number of other contentious issues ranging from gay marriage to civil rights.

In Fisher versus the University of Texas, the court will decide whether a white student, Abigail Fisher, was passed over unfairly for admission in 2008 because the school went too far with its affirmative action policy.

Another hot-button issue in the United States is same-sex marriage, and the court has at least eight appeals in line for consideration on this subject.

After long side-stepping the issue, Obama publicly endorsed gay marriage in May in a surprise move designed to draw a sharp contrast with Mitt Romney, his Republican rival in the November election who opposes same-sex unions.

Legal marriage between two men or two women is not recognized by the US federal government, but is now allowed in six of the 50 US states and in Washington, the US capital.