Australian defence force personnel could face the death penalty in Japan under a treaty between the two nations, a federal parliamentary committee has heard.
The Australia-Japan Reciprocal Access Agreement seeks to improve the ability of the countries' militaries to work together and with other key allies, including the US.
It also sets out a framework for troop activities in each country.
Under questioning, the Defence Department's Hugh Jeffrey told the joint standing committee on treaties that Australians who committed serious offences while in Japan could be sentenced to death under its judicial system, which includes capital punishment.
"The possibility that we think that Australian Defence Force personnel would be involved in such criminal activity we think is, is vanishingly small," he said.
"But were a person to commit such a terrible crime, while they are not on official duties, that the possibility is encompassed they could be subject to the death penalty."
He said negotiations were "challenging" and "complex" and were the first time Japan had ever held discussions for a military access agreement with another country since the end of the Second World War.
But finalising negotiations for the pact has taken seven and a half years, after the work was begun in 2014 by former prime minister Tony Abbott and his then-Japanese counterpart Shinzo Abe.
Japan's use of the death penalty has been a major stumbling block, amid fears Australians could be executed for criminal offences committed in Japan.
Mr Jeffrey said it wasn't "exceptional" that an Australian could be subject to the death penalty, because the nation had reciprocal agreements with other countries that also carried out capital punishment.
These countries included Papua New Guinea, the Philippines, Malaysia and Singapore.
The committee was told Australia had managed to secure exemptions from the application of the death penalty for its troops in some of those countries, including Papua New Guinea and the Philippines.
Labor senator Deborah O'Neill said she wasn't "convinced that our personnel are safe".
The next hearing into the agreement between Australia and Japan will be held in October.
