For decades, neutral Switzerland has played a key role in maintaining basic diplomatic contacts between Iran and the United States.

The foreign ministry in Bern said that in view of the war in the Middle East and the increasing security risk, it had "decided to temporarily close the Swiss embassy in Tehran".

Ambassador Olivier Bangerter and the remaining five other Swiss staff members left Iran by land earlier on Wednesday and will return to Tehran once the situation allows.

"As part of its good offices, Switzerland will continue to maintain an open line of communication between the United States and Iran, in consultation with the two countries," said the ministry statement.

Both the United States and Iran were informed of the temporary closure of the embassy and the departure of its Swiss staff.

"Switzerland will continue to be available to channel communications that the parties consider useful," the statement added.

"The protecting power mandate, under which Switzerland represents US interests in Iran, can be exercised independently of geographical location."

- The protecting power -

Renowned for its neutrality, Switzerland has been representing US interests in Iran since Washington broke off relations with Tehran after the 1980 hostage crisis, a year after the Iranian revolution.

In its role as the so-called protecting power, Switzerland has for decades allowed the two feuding nations to maintain a minimum of diplomatic and consular relations.

The Swiss embassy in Tehran handles all consular affairs between the United States and Iran, including passport requests, altering civil status and consular protection for US citizens in Iran.

Under the protecting power mandate, "Switzerland can either offer to act as a go-between on its own initiative or can fulfil this function at the request of the parties concerned, provided that all those involved agree," the foreign ministry says on its website.

The United States and Iran held a third round of indirect talks through Omani negotiators, on Iran's nuclear programme, in the Swiss city of Geneva on February 26.

Two days later, the United States and Israel launched the first wave of attacks in a war that has seen Iran strike targets in multiple countries around the Gulf.

Switzerland has called for de-escalation and a return to diplomacy.