US customs officials say Donald Trump has yet to issue any order extending Australia’s exemption from steel tariffs beyond 1 May, despite the government’s claim the exemption would be made permanent.

On 8 March the US president signed proclamations imposing a 25% tariff on imports of steel and a 10% tariff on aluminium. On 22 March the plan was qualified with a new instrument that stated Australia was one of a group of countries to be granted an exemption until 30 April “pending discussions of satisfactory long-term alternative means to address the threatened impairment to US national security”.

“By May 1, 2018, the president will decide whether to continue to exempt these countries from the tariffs, based on the status of the discussions,” the White House said.

Late on Friday, a spokesman for US Customs and Border Protection (CBP) confirmed that until 30 April the orders under section 232 of the Trade Expansion Act would not apply to Canada, Mexico, Australia, Argentina, South Korea, Brazil and member countries of the European Union.

“CBP will enforce the remedies imposed by the president under section 232 on imports of steel and aluminum from covered countries into the United States,” he said. “The exemptions are currently only effective through April 30. As of May 1st, if no presidential proclamation is issued, all countries listed will no longer be exempt.”

Earlier, US Customs advised it would “issue additional guidance on entry requirements for any products excluded from these measures, as soon as information is available”.

“CBP will also issue updated guidance if there are any changes to these measures, including any changes to exempted countries and any new requirements, such as quota requirements.”

No further CBP guidance or presidential proclamation has listed Australia as permanently exempt.

On Thursday the trade minister, Steve Ciobo, said Malcolm Turnbull had “secured an agreement with the US president that Australia will be exempt and that continues to be the case”.

He said the US had included Australia in the proclamation of a temporary exemption because it could not put in place separate instruments for every country.

Ciobo said the agreement was unconditional and it was “hard to imagine” a better deal that could be struck between the US and Australia.

Guardian Australia has contacted Ciobo and the Australian Department of Foreign Affairs and Trade to ask when and how they expect an unconditional exemption to be formalised.