Australia is considering a "serious and complex" request from the United States to help protect oil shipments against Iranian interference in the Persian Gulf.

Key points: The United States has been trying to convince allies to join an international coalition to protect shipping routes

The United States has been trying to convince allies to join an international coalition to protect shipping routes The requests have come following Iran's seizure of a British-flagged oil tanker

The requests have come following Iran's seizure of a British-flagged oil tanker Australian ministers vowed to keep the country's foreign policy relationship in lock-step with the US

At their annual Australia-US Ministerial Consultations (AUSMIN) talks in Sydney, the defence and foreign ministers of both countries met for discussions that spanned tensions with China over the South China Sea and a possible role for Australia in the Strait of Hormuz.

Defence Minister Linda Reynolds confirmed she and Foreign Minister Marise Payne had canvassed the US request at Sunday's meeting but that "no decision had been made".

"We are deeply concerned by the heightened tensions in the region, and we are strongly condemning the attacks on shipping in the Gulf," she said.

"The request the US has made is a serious and complex one, that's why we're giving this request serious consideration.

"We will ultimately as we always do, decide what's in our sovereign interests."

The US has been trying to convince allies to join an international coalition to protect shipping routes in the strategic passageway, following Iran's seizure of a British-flagged oil tanker.

The move came after British forces captured an Iranian oil tanker near Gibraltar, that the United Kingdom claimed was heading for Syria in a breach of European Union sanctions.

Describing the US-Australia alliance as "unbreakable", Secretary of State Mike Pompeo said he hoped the junior ally would partner with America on "some of the most pressing foreign policy challenges of our time" including "Iran's unprovoked attacks on international shipping in the Strait of Hormuz".

"I am very confident that we will have a global coalition," he said.

America's coalition-building efforts came after Iranian forces seized a British-flagged oil tanker. ( AP via Mehr News Agency: Morteza Akhoondi )

Australia vows to remain in lock-step with US

While waging so many disputes across vast areas of the globe simultaneously, the Trump administration is naturally drawing on as much support as it can garner from traditional allies, including Australia.

This year's round of AUSMIN talks was preceded by a bold announcement of the Pentagon's intentions to place intermediate-range missiles capable of flying around 1,000km in locations throughout Asia.

Secretary Esper had briefed travelling media on his flight to Sydney from Hawaii, that he would like to see the weapons deployed within "months", but did not say where they would be based or whether he had a more precise timetable in mind.

Since the Cold War, America had been bound by a treaty controlling the proliferation of such missiles, but formally withdrew from it on Friday last week.

Even without details on numbers and locations, signalling an intention to put batteries of US missiles in countries throughout the Asia-Pacific raises the prospect of an arms race between the US and its main rival, China.

US Secretary of State Mike Pompeo hoped Australia would partner with America on pressing foreign policy challenges. ( AP: Rick Rycroft/ Pool )

When asked about the issue, Foreign Minister Marise Payne did not rule out allowing American military hardware on Australian soil but emphasized that it was "not in anybody's interest for the Indo-Pacific to become more adversarial."

"The presence of the US and its military forces in this region has been a force for stability for decades and Australia has consistently welcomed that force and presence," she said.

The missile pronouncement is only the latest in a series of more belligerent statements the Trump administration is directing towards China.

On the sidelines of the ASEAN-centered East Asia Summit of foreign ministers, Mr Pompeo led the formulation of a tersely worded statement of a "Trilateral Dialogue" and secured the endorsement of his Australian colleague Marise Payne and Japan's Foreign Affairs Minister Taro Kono.

Without mentioning China by name, the ministers expressed "serious concerns about negative developments in the South China Sea" and cited "credible reports of disruptive activities in relation to long-standing oil and gas projects" in the region.

The trio "expressed strong opposition to any coercive unilateral actions that seek to alter the status quo and increase tensions in the area."

The statement was equally blunt on unnamed "countries and their proxies" which are "willing to pursue their objectives by undertaking malicious cyber activities" and the three countries agreed to deepen practical cooperation to better deter, mitigate, attribute, and counter malicious cyber activity, and provide clear and consistent messages of the consequences of such activities".

While the tone of the statement sits easily with the Trump administration's frequent verbal assaults on China and represents Japan's well-known views on Beijing, it is diplomatically brutal by the standards of Australian diplomacy and risks carrying consequences.

Secretary Pompeo continued that blunt rhetoric after the AUSMIN talks, saying the world had "watched for too long as China began to behave in ways it had not done before".

The US Defence Secretary went further, accusing Beijing of engaging in a "disturbing pattern of aggressive behaviour, destabilising behaviour".

"This includes using predatory economics and debt for sovereignty deals and promoting state-sponsored theft of other nations' intellectual property," he said.

Senator Payne's remarks were predictably more even-keeled towards Australia's most important trading partner.

"Admittedly, we have areas of difference with China," she said.

"We work closely with our key partners, with our strongest alliance partner, the US, and our key trading partner, China, to pursue those issues of stability and security and prosperity."

Australian foreign policy is built on trying to balance security alliances and shared concerns about China's rise with the economic interests of maintaining its relations with its biggest two-way trading partner.

Prime Minster Scott Morrison has stressed the importance of achieving both, most recently at a speech at the Asia Society in Sydney.

"The world's most important bilateral relationship — the US-China relationship — is strained. Trade tensions have escalated. The collateral damage is spreading," he said.

But with the Trump administration keen on placing missiles in US-friendly nations, and with Australia weighing its options for Persian Gulf naval patrols, Beijing's interest in how the Morrison Government balances its foreign policy has never been more intense.