US struggles to build willing coalition amid Hormuz tensions
Tensions have risen in the Gulf since the United States decided in May 2018 to withdraw from a landmark accord to limit Iran's nuclear programme and began to reintroduce sanctions.
But even as a series of ships have been seized in the narrow maritime thoroughfare - vital for the world's supply of crude - European countries have been reticent about a US plan to send in military escorts.
On Sunday, Australia became the latest ally seeming to give the plan a wide berth.
Australian defence minister Linda Reynolds told the visiting US secretaries of state and defence that their "very serious" and "complex" request would be given "very serious consideration" - but stopped short of offering a full response.
"We are deeply concerned by the heightened tensions in the region. And we strongly condemn the attacks on shipping in the Gulf of Oman," said Reynolds.
"But we will ultimately, as we always do, decide what is in our own sovereign interests," she told Mike Pompeo and the newly confirmed Pentagon chief Mark Esper who was on his maiden overseas trip.
"And we'll certainly discuss this issue during our ministerial consultations, but again, no decision has yet been made."
Washington floated the idea of a naval coalition in June, after multiple attacks on ships in the Gulf, which the United States had blamed on Iran - but which Tehran denies.
The plan was to have each country provide a military escort for their ships, with US military providing a security backstop, monitoring the zone of operations and providing command and control.
Asked by a reporter about the lack of enthusiasm from Australia, Pompeo was characteristically combative and insisted he was "very confident that we will have a global coalition".
"There's lots of conversations taking place, amongst all the countries, as with Australia," he said.
Esper, meanwhile, said the United States had gotten "various degrees of response", adding "I think there'll be some announcements coming out in the coming days".
Referencing the prospect of European-only cooperation, Esper plaid down a bifurcation of effort.
"I think the purpose remains the same whether it's an operation conducted under the United States command and control, or conducted by somebody else, a European partnership.
"I think both fulfil the same purpose, a unity of effort with regard to ensuring freedom of navigation."
Paris, Berlin and London plan to coordinate and share information in the Gulf to reinforce maritime security, but without deploying additional assets, according to French Defence Minister Florence Parly.
"We are trying to organise ourselves as Europeans, but one thing is certain: our actions will have only one objective, to lower current tensions and defend our interests," she said.
Germany has distanced itself from a military operation in the Strait of Hormuz, considering it could hinder European efforts to reach a diplomatic solution with Iran.
German government spokeswoman Ulrike Demmer said last week said the focus should be on "diplomacy and de-escalation" amid a spike in tensions between the UK and Iran.
Declaring the German government "reluctant" to get involved in the US plan she said that "participation in a US-led mission could complicate this issue, even as of course we share the goal of freedom of navigation."
Britain has responded to the seizure of a UK tanker in June by announcing it would escort British-flagged ships and send a second warship to the region.