Tens of thousands of government supporters rallied today, state media said, and a reformist party called on Iran's rulers to apologise to the nation two days after eight people were killed in anti-government protests.
The rallies today called for the punishment of opposition leaders for fomenting unrest after June's disputed presidential poll which was won by hardliner Mahmoud Ahmadinejad, state media reported.
The elite Revolutionary Guards accused the foreign media of joining hands with the opposition to harm the Islamic state and the British ambassador to Tehran was summoned by the Iranian government to be accused of "interference" in state matters.
"If Britain does not stop talking nonsense it will get a slap in the mouth," Iranian Foreign Minister Manouchehr Mottaki said. The British government said their envoy would respond "robustly" to any criticism.
The establishment intensified a crackdown on the reform movement on Sunday by rounding up leading moderates to try to end street protests after the deadly weekend clashes erupted during the Shia Muslim religious ritual of Ashura.
At least 20 opposition figures have been arrested since Sunday, including three senior advisers to opposition leader Mirhossein Mousavi, his brother-in-law and a sister of Iranian Nobel Peace Prize winner Shirin Ebadi, opposition websites reported.
Ms Ebadi confirmed her sister's arrest.
Political turmoil has entered a new phase in Iran with bloody face-offs and arrests, with security forces calling on authorities to deal "firmly" with opposition leaders.
"Trying to overthrow the system will reach nowhere ... designers of the unrest will soon pay the cost of their insolence," the Revolutionary Guards said in a statement. "The opposition, which has joined hands with the foreign media, is backed by foreign enemies."
In a heated war of words, the reformist Islamic Iran's Participation Front said in a statement: "The only way out of the current crisis is for the authorities to respect the law and apologise to the nation."
Tens of thousands of people today chanted "We are ready to sacrifice our lives for our Supreme Leader (Ayatollah Ali Khamenei)", state television reported, saying the nationwide demonstrations had taken place spontaneously.
"Demonstrators demand the punishment of those behind Sunday's protests which insulted religion," state television reported, referring to the protests taking place during Ashura.
Iranian authorities say eight people were killed in clashes on Sunday when supporters of Mousavi used the Ashura religious festival to stage fresh anti-government rallies.
Reuters