Iran's relations with the West have been deteriorating since the shock presidential election win in June of Mahmoud Ahmadinejad, a straight-talking hardliner determined to restore Islamic revolutionary values.
The clerical regime is accused of using an atomic energy drive as a cover for weapons development - a charge it denies - and last week Ahmadinejad drew international condemnation for calling for Israel to be "wiped off the map".
Foreign Minister Manouchehr Mottaki said "some 40 ambassadors or heads of mission" - or close to a third of those in such posts - would be coming home in the coming months. Those set to go include Iran's ambassadors in London, Paris, Berlin and Geneva. Tehran's ambassador in London, Mohammad Hossein Adeli, has only served for a year.
Despite talk of a major purge of moderates, Mottaki asserted the changes as "normal" and insisted many of the diplomats, appointed by former reformist President Mohammad Khatami, were close to retirement.
But some had been engaged in long-running talks with Britain, France and Germany aimed at resolving the nuclear row, and were criticised by hard-liners for being too weak.
These talks broke down in August when hard-liners in Tehran rejected an EU offer of trade and other incentives in exchange for a cessation of fuel work and resumed uranium conversion, a precursor to ultra-sensitive enrichment work.
Western diplomats said that some of those being changed had also been involved in secret contacts with the United States following the US invasion of Afghanistan and until shortly after the invasion of Iraq.
British Prime Minister Tony Blair has blamed Iran for a series of attacks against British troops in southern Iraq, and Britain was behind a UN Security Council statement which condemned Ahmadinejad's anti-Israel remark.
"The Iranian government has got to understand that the international community simply will not put up with their continued breach of the proper and normal standards of behaviour that we expect from a member of the United Nations," Blair said on Wednesday, nevertheless asserting that "nobody is talking about military threats or invasion of Iran."
In return, Iran says it has proof of British involvement in a string of bombings in the restive south-western oil province of Khuzestan, which borders areas of southern Iraq patrolled by British troops.
British imports have also been blocked by Iran in apparent retaliation for Britain's position in the nuclear row. Iran has denied the formal imposition of sanctions but has asserted it will link its trade policy to foreign relations.
Iran is facing the risk of being referred to the UN Security Council over its nuclear programme, after the International Atomic Energy Agency (IAEA) last month found it to be in "non-compliance" with the nuclear Non-Proliferation Treaty (NPT).
The UN nuclear watchdog will next discuss Iran on November 24.