At least 25 jurisdictions have decided to suspend package deliveries to the United States, as concern grows over the impact of President Donald Trump's looming tariffs, a UN body said Tuesday.

The Trump administration said late last month that it will abolish a tax exemption on small packages entering the United States from August 29.

The move has sparked a flurry of announcements from postal services, including in France, Britain, Germany, Italy, India, Australia and Japan, that most US-bound packages would no longer be accepted.

The United Nations' Universal Postal Union said it had already been advised by 25 members that their postal operators "have suspended their outbound postal services to the US, citing uncertainties specifically related to transit services".

It said the suspensions will remain in place until there is more clarity on how US authorities plan to implement the announced measures.

The UPU did not provide a list of postal services it had heard from.

The organisation, which was established in 1874 and counts 192 members, warned that the new US measures would "entail considerable operational changes for postal operators around the world".

From Friday, the UPU said the measures would require postal carriers delivering packages to the United States "to collect customs duties from senders in advance", on behalf of the US Customs and Border Protection agency.

India's communications ministry said at the weekend that Trump's executive order issued last month requires transport carriers or other "qualified parties" approved by US authorities to collect and remit the tariff duties.

But "several critical processes relating to the designation of 'qualified parties' and mechanisms for duty collection and remittance remain undefined," it said in a statement.

Under the new US measures, individual customers will still be able to send documents and items worth up to US$100 as presents to the country without being taxed.

But anything above that value is expected to be hit with the same tariff rates applied to other imports from the sending country.

The UPU stressed that it was "taking all possible measures to prepare its member countries for the impacts (the new measures) may have on their postal flows".

UPU chief Masahiko Metoki had sent a letter to US Secretary of State Marco Rubio on Monday to convey member countries' concern regarding the operational disruptions, it said. (AFP)