Postal traffic to the United States plunged more than 80 percent following Washington's imposition of new tariffs, with 88 operators worldwide fully or partially suspending services, the Universal Postal Union said Saturday.

The UPU, the United Nations' postal cooperation agency, is working on "the rapid development of a new technical solution that will help get mail moving to the United States again", its director general Masahiko Metoki said in a statement.

US President Donald Trump's administration announced in late July that it was abolishing a tax exemption on small packages entering the United States from August 29.

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

The UPU said data exchanged between postal operators via its systems showed that traffic to the United States was down 81 percent on August 29, compared to a week earlier.

"Furthermore, 88 postal operators informed the UPU they have suspended some or all postal services to the US until a solution is implemented," it said.

These included operators in 78 UN member states -- including two in Bosnia and Herzegovina -- and in nine other territories including Macau and the Cook Islands.

- New system upcoming -

The US changes places the burden of customs duty collection and remittance on transport carriers or "qualified parties" approved by the US Customs and Border Protection agency.

"Carriers, such as airlines, signalled they were unwilling or unable to bear this responsibility," while postal operators had not yet established links to those approved parties, "causing major operational disruptions", said the UPU.

The UN agency said it was working on a "Delivered Duty Paid" solution which will soon be integrated into its customs declaration platform.

It enables post operators "to calculate and collect the required duties from customers at origin", the agency said.

In the meantime, the UPU said that, as of Friday, postal operators could access a calculator via a software interface that can be plugged into their retail and counter systems.

- Letter sent -

Metoki has written to US Secretary of State Marco Rubio to convey member countries' concerns surrounding the upheaval.

UPU figures show that over the past 12 months, inbound traffic to the United States, from all categories of mail, comprised 15 percent of global postal traffic.

Of that, 44 percent came from Europe, 30 percent from Asia, and 26 percent from the rest of the world.

The majority was likely to be small packages -- the international mail product most often used for e-commerce goods, said the UPU.

Based in the Swiss capital Bern, the UPU was established in 1874 and counts 192 member states. It sets the rules for international mail exchanges and makes recommendations to improve services.