SYDNEY (AFP) - The Australian and British foreign ministers on Sunday slammed the killing of a Japanese journalist by the Islamic State in Iraq and Syria (ISIS) as they vowed to tackle the militant threat at defence talks in Sydney.

British Foreign Minister Philip Hammond is in Australia for the annual meeting with his counterpart Julie Bishop, with efforts to counter terrorism and foreign fighters high on the agenda. "I wanted to extend Australia's deepest condolences to the people and government of Japan," Ms Bishop told reporters.

"The depraved behaviour that has led to the killing of two Japanese nationals is an unspeakable atrocity and we are united in our resolve to counter terrorism in all its forms wherever it occurs."

Mr Hammond echoed the Foreign Minister's words and said the allies were committed to combating the "growing challenge of Islamist extremism seeking to break down the structures of nation states".

ISIS claimed in a video released online that it has killed a Japanese hostage, the second beheading of a Japanese captive in a week.

Earlier on Sunday, Australian Prime Minister Tony Abbott condemned the purported killing as a "terrible shock" for Japan.

"This just demonstrates how important it is that all countries do what they reasonably can to disrupt and degrade this death cult which has ushered in a new dark age over parts of the Middle East," he said.

Also on the agenda was Russia, with Mr Hammond describing Moscow's actions in Ukraine as "ignoring all the rules of the post-Cold War settlement", and the fight against the spread of the Ebola epidemic.

Australia is helping to staff a 100-bed British-built Ebola treatment centre in Sierra Leone.

The pair will be joined by Britain's Defence Secretary Michael Fallon and his Australian counterpart Kevin Andrews in Sydney on Monday.