President Donald Trump accused Iran of duplicity over the status of negotiations, saying Tehran had sought talks while publicly denying any discussions were taking place, in a post on August 3.

The clash over whether the two sides are talking at all points to the fragility of a diplomatic track that has repeatedly stalled since a ceasefire collapsed in mid-July, with the Strait of Hormuz and Iran's nuclear programme still unresolved and a US naval blockade choking Iranian oil exports..

Trump said Iran had asked for a meeting, with more talks scheduled, then stated openly that nothing was being discussed and that it was dealing only with Oman.

Trump said the Strait of Hormuz was already controlled by the United States Navy through what he called a blockade, and that nothing would reach Iran unless a deal or "Total Surrender" was reached. He rejected Iran's assertion that it would operate the strait, and repeated that Iran would never be allowed a nuclear weapon.

Iran's foreign ministry spokesman Esmail Baghaei said there was no immediate plan for negotiations with the United States, reiterating that Tehran was engaged only with Oman over the strait. Baghaei attributed the waterway's closure to the US naval blockade and what he described as Washington's breach of its commitments, and said the strait would not return to its pre-war status.

Iran and Oman are reported to be in the final stages of talks over a temporary shipping route through the strait, which handled around a fifth of global oil supply before the war. Oil fell on signs of progress, with Brent crude down about 4.5%.

Switzerland is in contact with all parties over any possible negotiations between Iran and the United States and is ready to offer its services if the sides want them, its foreign ministry said, RIA Novosti reported on August 3.

The Swiss position keeps Bern in play as a potential venue and facilitator months after a US-Iran memorandum it had prepared to host fell through, at a moment when Washington says talks are imminent while Tehran insists it is dealing only with Oman over the Strait of Hormuz.

Asked whether Switzerland intended to host negotiations again on its soil, foreign ministry spokesman Pierre-Alain Eltschinger said the country was in contact with all the states involved and stood ready to provide services if both sides wished.

Asked whether such talks could again be held at Bürgenstock, in central Switzerland, or in Geneva, Eltschinger said the ministry did not comment on details. Switzerland had said in June that a memorandum between Iran and the United States would be signed at Bürgenstock, in canton Nidwalden, though that did not take place and the sides later signed virtually.