Myanmar villagers have sued the California-based oil titan claiming it was complicit in human rights abuses by the Southeast Asian country's brutal military junta, including forced labour, rape and torture.

The trial in Los Angeles stems from two lawsuits filed by up to 15 unidentified villagers from the nation formerly known as Burma over the construction of the 62-kilometer (39-mile) Yadana natural gas pipeline.

The villagers claim in their seven-year-old lawsuit that Unocal turned a blind eye as junta troops murdered, raped and enslaved villagers and forced them to work on the 1.2-billion-dollar pipeline in the 1990s.

"Burmese soldiers enforced a system of slave labour and committed horrible acts of violence on Unocal's behalf," said Terry Collingsworth, executive director of the International Labor Rights Fund, which represents some of the villagers.

Unocal, which did not directly operate the field that was owned by the Myanmar government, strongly denies any involvement in abuses.

The case centres on the construction of the much-disputed pipeline, built by Unocal and partners including France's Total, to carry natural gas from Myanmar to neighbouring Thailand.

The villagers are suing for unspecified damages alleging that Unocal benefited from use by the Yangon junta of forced labour and its soldiers' use of murder and rape, even if it did not agree with the abuses.

At issue in the first part of the complex trial is whether Unocal can be held liable for the conduct of its subsidiaries which invested in the pipeline.

Daniel Petrocelli, Unocal's lead lawyer, said California's "alter-ego doctrine" bars plaintiffs from trying to tap a parent corporation if a subsidiary has valuable assets of its own.

"The whole case boils down to one point: If the subs (subsidiaries) can pay, the case goes away," he told a crowded courtroom in opening arguments.

But lawyers for the villagers maintain that Unocal is using its subsidiaries as corporate shells to avoid responsibility in the case.

"Unocal's opening statement was a tribute to the ability of corporations to do whatever they want in the name of profit," Dan Stormer, attorney villagers, told AFP.

"Nothing about these various entities was independent," he said adding that Unocal should be held directly responsible for its units' role in the affair as they were sham companies.

But Petrocelli insisted the units -- Unocal Myanmar Offshore Co., Unocal International Pipeline Co. and Unocal Global Ventures -- had hundreds of millions of dollars in assets and their own corporate structures.

"Every one of these companies has the ability to pay," Petrocelli said.

In July, Judge Victoria Chaney rejected Unocal's arguments that the case should be tried at least in part under the laws of Myanmar or Bermuda, where its subsidies were based, instead of under US law.

If Unocal manages to convince the court in the first phase of the trial, which is expected to last about 20 days, that its subsidiaries, rather than the parent company, should be targeted by any suits, it could move to have the abuse charges thrown out in the second phase of the trial.

In written complaints, the villagers said they were pressed into service to clear a route and build facilities for the pipeline, widely described as the largest foreign-invested project in Myanmar.

The plaintiffs' identities have been concealed for fear of reprisals by Myanmar's junta.

Unocal executives have acknowledged that troops did force villagers to carry ammunition and supplies for the military and to perform other labour in the vicinity of the project, but deny that any of the labour was linked to the pipeline's construction.

Unocal owned the pipeline jointly with Total, formerly TotalFinaElf, and the Thai and Myanmar governments. Total is being sued separately in Europe.