The head of France's domestic intelligence service (DST) has said an Iranian opposition group was planning to attack Iranian embassies across Europe.
Two women were rushed to hospital with severe burns
The allegation came as scores of supporters of the People's Mujahideen protested outside the DST headquarters in Paris against the arrest of 159 members of the French-based group on Tuesday.
Three Iranian demonstrators set themselves on fire, while in the Swiss capital, Berne, police prevented another man from setting himself on fire outside the French embassy.
Iran has welcomed France's crackdown on the People's Mujahideen, an armed group which seeks the overthrow of the Islamic regime.
Iran's reformist President Mohammad Khatami, meanwhile, has broken his silence on the series of disturbances that have shaken the capital, Tehran, over the past week.
Mr Khatami said such protests were normal in a democratic society, but they should be both carried out and dealt with within the law.
Iraq base squeezed
DST chief Pierre de Bousquet de Florian said the People's Mujahideen "had the intention to commit attacks outside Iran, including in Europe, against Iranian interests and even against diplomatic representations".
He said the group was "transforming its Val d'Oise centre [in Paris]... into an international terrorist base".
The People's Mujahideen has been classified as a terrorist organisation by the United States and the European Union, although it maintains offices in several western European cities.
The BBC's Caroline Wyatt in Paris says until recently, the People's Mujahideen had its main armed bases within Iraq, just across the border with Iran, but the United States has been trying to disband those camps.
Our correspondent says there have been fears in France that as a result, the group would shift more of its activities to Europe.
All but 26 of those detained in the raids in Paris have been released.
Demonstrators believe those being held include Maryam Rajavi, wife of the People's Mujahideen leader, Massoud Rajavi.
Although protests in Teheran have apparently been diminishing, there are reports that the unrest has spread to a number of provincial cities.
The BBC's correspondent in Tehran, Jim Muir, says it is undoubtedly President Khatami's own inability to deliver the reforms for which millions of Iranians voted that has produced this latest wave of protests.
President Khatami acknowledged the demonstrators' "right to protest, which existed in the past and still exists", but said violence from whatever quarter would not be tolerated.
He also criticised America's declaration of support for the protesters as an "incorrect... act of interference" in Iran's affairs.