SYDNEY — Australia will join the US-led mission to protect shipping through the Strait of Hormuz amid heightened tensions with Iran, Prime Minister Scott Morrison announced on Wednesday.

Morrison said Australia would send a "modest" contribution -- including a frigate, a P8 maritime surveillance aircraft and support staff -- to the mission, which will also involve British and Bahraini forces.

"Our contribution will be limited in scope and it will be time-bound," Morrison said, expressing concern about security incidents in the vital shipping lane in the past few months.

"This destabilising behaviour is a threat to Australian interests in the region," he said in a joint statement with his foreign and defence ministers.

US Secretary of State Mike Pompeo and Defense Secretary Mark Esper had pressed for Australia's help patrolling the strategic waterway during a visit to Sydney earlier this month.

The move followed a spate of incidents -- including the seizure of ships -- involving Iran and Western powers, in particular Britain and the US, centred on the vital Gulf channel.

Defence Minister Linda Reynolds said Australian military staff would in coming weeks join the security operation's headquarters in Bahrain, which announced its involvement in the operation on Tuesday.

The P8 Poseidon aircraft will patrol the region for a month, later in the year. The frigate, with a crew of some 170, will not be deployed to the joint operation until January and take part for six months, she said.

Morrison stressed that the deployment would be "modest, meaningful and time-limited" while defence experts said it was likely a "re-tasking" of planned deployments to the region to satisfy US requests.

The US had been struggling to piece together an international coalition to protect cargo ships travelling through the Gulf, with allies concerned about being dragged into conflict with Iran.

Britain eventually agreed to participate two weeks ago, and Morrison's government has debated the move since Pompeo and Esper made their direct appeal at the beginning of the month.

US President Donald Trump has been trying to mount a campaign of "maximum pressure" against Tehran since he withdrew the US from a landmark 2015 deal placing curbs on Iran's nuclear programme and began reimposing sanctions, urging reluctant Western allies to follow suit.

But European countries have declined to join the maritime security force for fear of harming European efforts to rescue the nuclear treaty.

Iran has seized three tankers in strategic Gulf waters since last month, including a British-flagged vessel.

That came after British Royal Marines helped impound a tanker carrying Iranian oil off the British overseas territory of Gibraltar on July 4.

Britain suspected it was destined for Syria in defiance of European Union sanctions, which Iran denies.

The US and its Gulf allies have also accused the Islamic republic of carrying out several mysterious attacks on ships in the region. Tehran has denied involvement. — AFP