A bomb has exploded in Tehran at the shrine of Iran’s revolutionary founder as thousands of people protest at the result of the country’s election, reports say.

Riot police in Tehran (Pic: Twitter user Madyar)

At least one person was killed and two others injured in the northern wing of Ayatollah Ruhollah Khomeini’s shrine, said the Fars news agency.

Reports said it was a suicide bombing and the attacker died in the blast.

Elsewhere in the Iranian capital, police have been using tear gas and water cannon on protesters, according to witnesses.

Reports said many people have defied Government warnings that any protests would be suppressed.

Eyewitnesses say some 3,000 protesters chanted “Death to the dictator!” and “Death to dictatorship!” near Revolution Square in the city centre.

Riot police were sent out on to the streets following a demand by Iran’s supreme leader for the demonstrations to end.

Foreign media are banned from reporting on non-official events but reports are still reaching the outside world of violence being used by the authorities.

Earlier, the head of the police warned pro-reformer Mirhossein Mousavi of “firm action” against any “illegal” demonstration.

Supreme Leader Ayatollah Ali Khamenei issued a strong warning on Friday to the leaders of the street protests that they would be responsible for any bloodshed.

Mr Khamenei said the June 12 vote was won fairly by hardline President Mahmoud Ahmadinejad, who beat Mr Mousavi by a landslide.

The result sparked fury among supporters of the losing candidates, who accused the government of rigging the poll and took to the streets in their hundreds of thousands in the biggest public protests since the 1979 Islamic revolution.

Iran’s electoral watchdog, the Guardian Council, says it is ready to “randomly” recount up to 10% of the ballot boxes from the election, state TV said.

In his speech, Mr Khamenei also denounced Britain as the “most treacherous” of Iran’s enemies.

British Foreign Secretary David Miliband has said violence on the streets of Tehran must not be turned into a battle between Iran and the UK.

Writing in The Sun, he hit back at the Ayatollah’s claims. “Dignity has been shown by the protesters on the streets of Tehran,” Mr Miliband said.

“Ayatollah Ali Khamenei tried to blame the unrest on the West.

“But we will not allow anyone to turn scenes on the streets of Tehran into a battle between Britain and Iran. My message to the Iranian people is simple: the future of your country is for you to decide.

“But we need to know whether Iran is prepared to work with us to restore confidence in its nuclear intentions.”

The Ayatollah offered no concession to opposition supporters who are demanding the elections be cancelled and held again, sternly warning against further protests.

He blamed Great Britain and Iran’s external enemies for the unrest, vigorously defending the ruling system.

“The enemies (of Iran) are targeting the Islamic establishment’s legitimacy by questioning the election and its authenticity before and after (the vote),” the Ayatollah continued.

British Prime Minister Gordon Brown, talking to Sky’s political editor Adam Boulton, said: “What we want is to have a good relationship with Iran in the future.

“But that depends on Iran being able to show to the world that its elections have been conducted fairly and that there is no unfair suppression of rights and individuals in that country.”

Supporters of runner-up Mr Mousavi have so far ignored the Ayatollah, holding huge unauthorised rallies.

Election Protests: Live Inside Iran

Tens of thousands of Iranians had gathered in and around Tehran University to hear Khamenei’s Friday prayer sermon.

Some in the crowd were draped in Iranian flags. Others held placards with anti-Western slogans.

As passions soared, the crowd reportedly chanted: “Death to the UK, Israel and the US.”

American President Barack Obama said he was very concerned by the “tenor and tone” of Khamenei’s comments.

In a US TV interview, Mr Obama said that Iran’s government should “recognise that the world is watching.”

He said “how they approach and deal with people who are, through peaceful means, trying to be heard” will signal “what Iran is and is not”.

Mr Khamenei’s speech followed six days of protests by Mousavi supporters.

On Thursday, tens of thousands of black-clad marchers bore candles to mourn those killed in earlier rallies.

Iranian state media has reported seven or eight people killed in protests since the election results were published on June 13.

Scores of reformists have been arrested and authorities have cracked down on both foreign and domestic media.