Troops, planes and warships to help guard strait in Middle East where tensions are flaring with Iran, but critics warn involvement could breach international law.
Australian forces will make a “modest, meaningful and time-limited” contribution to a United States-led mission in the Strait of Hormuz aimed at protecting freedom of navigation in the Gulf region.
Labor has supported the new mission as “appropriate”, but critics are warning the involvement of Australia’s military in the region could be seen as an “act of aggression” in breach of international law.
The prime minister, Scott Morrison, announced on Wednesday that Australia would send forces to the Middle East because “destabilising behaviour” in the Gulf was a threat to Australian interests.
“The government has been concerned over incidents involving shipping in the Strait of Hormuz over the past few months,” Morrison said.
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“This destabilising behaviour is a threat to our interests in the region, particularly our enduring interest in the security of global sea lanes.
“The government has decided it’s in Australia’s national interests to work with our international partners to contribute to an international maritime security mission … in the Middle East.”
Morrison said about 15% of crude oil and 30% of refined oil destined for Australia came through the Strait of Hormuz, meaning instability in the region was also an economic threat that needed to be confronted.
“Freedom of navigation through international waters is a fundamental right of all states under international law,” he said.
“All states have a right to expect safe passage of their maritime trade consistent with international law.”
Australia has committed a frigate, surveillance and patrol aircraft and personnel to the Middle East as part of the US-led mission, known as the international maritime security construct (IMSC).
The United Kingdom and Bahrain are the only other countries to join the US in the Strait of Hormuz, but the UK has appealed to European allies to join the mission to safeguard shipping lanes.
Australian defence force members will join the IMSC taskforce based in Bahrain, which hosts the US navy’s central command and fifth fleet.
The defence minister, Linda Reynolds, said the Royal Australian Air Force would send a P-8A poseidon maritime surveillance aircraft to the region for one month before the end of 2019, while an Australian frigate would be present for six months from January.
“Australia’s core interest in this mission is de-escalation,” Reynolds said.
“The announcement today is clearly in Australia’s national interest and we’re very proud to be working with our allies and our friends to promote the global rules-based order and also the rule of law.”
Labor’s shadow minister for defence Richard Marles said the opposition supported the commitment on the basis that it was “tightly framed” around freedom of navigation for commercial shipping in the Gulf.
“This is an appropriate measure for Australia to take,” Marles said.
The commitment to join the US comes after tensions simmered in the region over the seizure of an Iranian ship by Gibraltar, with the backing of the UK, that was believed to be heading to Syria in breach of UN sanctions.
The US and Iran have been engaged in brinkmanship in the Gulf since the US withdrew from the Iran nuclear deal in May 2018, after which the US announced a “maximum-pressure” strategy on Tehran.
Former secretary of the defence department, Paul Barratt, told the Guardian Australian involvement in potential military action in the Gulf could be illegal, and argued it was “very foolish for us to get involved in this provocative behaviour”.
“This is an application of military force. There ought to be a debate in the parliament, and we ought not to engage in any activity that would foreseeably involve the use of military force without that debate.”
In correspondence with the prime minister, Barratt, now president of Australians for War Powers Reform, argued that in the absence of any credible threat to Australia or an authorising resolution of the UN security council, any Australian involvement in attacks on Iran would be an act of aggression and therefore illegal.
“We appeal to you for a debate in our parliament on the growing tensions between the US and Iran, and steps which Australia could take to reduce them. Such a debate and a vote by all our elected representatives, and authorisation by the governor general, as the only person with the constitutional power to authorise the deployment of the ADF into international armed conflict, must be absolute prerequisites before any military action is undertaken.”
In response to Barratt, assistant minister to the prime minister, Ben Morton, said the Australian government was deeply concerned by current tensions in the Middle East. “A deterioration in the situation would be counter to regional security, global trade and the best interests of Australia and the world. We have urged Iran to refrain from escalatory action.”
Morton said the Australian government supported the Joint Comprehensive Plan of Action, “which serves the international community’s interests in non-proliferation”.