In an unexpected diplomatic move, Iran has rejected Britain's choice of its ambassador to Tehran.

The rejection of London's choice for its next ambassador to the Islamic republic comes Friday amid what many diplomatic observers have said were improving relations between Britain and Iran.

After years of isolation, Britain's Foreign Secretary, Jack Straw, has made two trips to Tehran in recent months in the wake of the September 11 terrorist attacks in the United States.

Those visits were the first by a man in his position in the British government since the fall of the Shah in 1979.

London's choice for ambassador, David Reddaway, has been denounced in the conservative newspapers in Iran. The papers call Mr. Reddaway a Jewish member of the British foreign intelligence service.

The British government says he is neither Jewish nor an employee of its overseas spy service.

Mr. Reddaway's wife is Iranian by birth, leading some analysts in London speculating that she may be the reason for the refusal. Mr. Reddaway speaks Farsi - Iran's main language - and he has served twice before as a diplomat in Tehran.

As recently as last month, Prime Minister Tony Blair discussed the selection of the British ambassador with Iran's President Khatami.

But analysts in London believe the diplomatic rebuff could represent the internal power struggles going on in Tehran. They believe the move is also tied to London's close links with Washington since the September 11 terrorists attacks.

President Bush denounced Iran in his recent State of the Union address for being part of what he called an "axis of evil" along with Iraq and North Korea.

Britain will now be represented in Tehran by a charge d'affairs.

Diplomatic observers say it is hard to see how the current British-Iranian diplomatic rift can be resolved since London says it has no plans to forward another person to fill the vacant ambassadorial position.