The prime minister of East Timor, Mari Alkatiri, says Australia is unlawfully exploiting the resources of the sea between the two countries.
Mr Alkatiri was speaking as negotiations resumed in the East Timorese capital, Dili, aimed at settling the dispute over the maritime border between Australia and East Timor, and the ownership of billions of dollars in offshore oil and gas revenues.
East Timor argues that the border should be at the midway point between the countries, in line with international practice.
It says it might not ratify a joint agreement to exploit the richest oil field in the area if Australia does not negotiate in good faith.
But the Australians want to keep the present border agreed with Indonesia, from which East Timor gained independence in 2002.
The current border gives them control over most of the oil and gas fields.
From the newsroom of the BBC World Service