Iran cleric says UK embassy staff may face trial

In London, a Foreign Office spokeswoman said: "We are very concerned by these reports and are investigating."

The spokeswoman added: "Allegations that our staff are involved in fomenting unrest are wholly without foundation. We will be seeking an urgent explanation from the Iranians."

She said British authorities were speaking to the Iranian embassy in London and to Iranian officials in Tehran.

On Wednesday, Iran's semi-official Fars News Agency said that one of those detained "had a remarkable role during the recent unrest in managing it behind the scenes."

It said another embassy employee had been a "main element behind the riots" but had been freed because she had diplomatic immunity.

Iranian officials deny the election was rigged, saying it was the nation's "healthiest" since the 1979 Islamic revolution.

The authorities have portrayed the unrest as the work of local subversives and foreign powers, especially Britain.

Jannati reiterated accusations by other senior Iranian figures that the West had planned a so-called "velvet" revolution to undermine the Islamic Republic's establishment.

"They (the British) had ahead of time ... announced that in the election that is scheduled to take place in Iran there might be unrest and turmoil," Jannati said.

(Reporting by Hashem Kalantari in Tehran and Luke Baker in London; Writing by Fredrik Dahl; Editing by Dominic Evans)