Iran threatened tougher action against protesters Tuesday and hard-liners on motorcycles harassed the top opposition leader at his office Tuesday, signs of a possible intensified crackdown after the biggest anti-government demonstrations in months.

The warning suggested that authorities fear that the protest movement launched after disputed presidential elections in June could pick up new steam. The demonstrations Monday turned into fierce clashes between youths throwing stones and riot police and militiamen wielding batons and tear gas, and more than 200 protesters were arrested.

Perhaps more importantly, the demonstrators showed an increased fervor and boldness, openly breaking the biggest taboo in Iran, burning pictures of Supreme Leader Ayatollah Ali Khamenei and chanting slogans against him.

Iran's top prosecutor, Gholam Hossein Mohseni Ejehi, warned the judiciary will take a new no-tolerance policy toward protesters — even as students held a new, small demonstration at Tehran University on Tuesday.

"So far, we have shown restraint. From today no leniency will be applied," Ejehi said, according to the official IRNA news agency.

He demanded Tehran prosecutors take stronger action against those "who violate public order and damage public properties." When asked if prosecutors will pursue the top opposition leader, Mir Hossein Mousavi, he said, "We will not tolerate anyone who commits actions against security, and we will confront them," according to the Fars news agency.

Plainclothes men on motorcycles — likely hard-line Basiji militiamen — confronted Mousavi at his Tehran office on Tuesday. Up to 30 men on motorcycles, some in masks, blocked Mousavi as he tried to drive out of his office garage and chanted slogans against him, two opposition Web sites said, citing witnesses.

Mousavi got out of his car and shouted at them, "You're agents. Do whatever you've been ordered to do, kill me, beat me, threaten me," before his aides hustled him back inside, the Gooya News Web site reported. The men left several hours later and Mousavi was able to leave.

Hard-line clerics and commanders of the elite Revolutionary Guard have called for the arrest of Mousavi, accusing him of sparking protests and conspiring against Iran's clerical leadership. Arresting Mousavi or other top opposition leaders would be a major escalation, likely to spark greater turmoil — and so far the government has balked at taking the step.

On Tuesday, riot police were out in heavy numbers at intersections on major thoroughfares around the city.

At Tehran University, a group of hard-line Basij militiamen attacked a small demonstration of students Tuesday. The militiamen pelted them with stones and fired tear gas to disperse them and dragged at least one student away, said witnesses, who spoke on condition of anonymity fearing retribution.

Tehran's police chief, Gen. Azizullah Rajabzadeh, announced that 204 protesters, including 39 women, were arrested in the capital during Monday's demonstrations. They were detained for "violating public order," including setting fire to vehicles and chanting slogans, he said, according to the state news agency IRNA.

Those arrested will be handed over to the judiciary for prosecution, he said. There was no immediate word on the number of arrests outside Tehran.

The turnout in Monday's protests — fueled by students marching by the thousands on more than a dozen campuses around the country — showed that months of arrests and government intimidation had failed to stamp out the movement.

A wave of arrests since July succeeded in crushing the massive protests by hundreds of thousands that erupted after the election, which the opposition says Mousavi won but President Mahmoud Ahmadinejad stole by fraud.

More than 100 politicians, activists and protesters have been put on a mass trial before the Revolutionary Court, accused of being part of a foreign-backed plot to overthrow the Islamic Republic. Five have been sentenced to death and 80 others to prison terms up to 15 years. In recent weeks, more than 100 student leaders were arrested ahead of Monday's demonstration, and several have been given heavy prison sentences.

Since the summer, the opposition has held major protests only about once a month — timed to coincide with the many occasions on Iran's political and religious calendar that traditionally bring street demonstrations. The strategy aims to drum up as many people as possible and draw more attention.

Authorities may be concerned because the coming months could heat up, with several key occasions that give the opposition a pretext for bringing supporters into the street.

In mid-December, the Islamic holy month of Moharram begins — and throughout the month Iranians traditionally hold mass mourning ceremonies. Next comes the anniversary of the 1979 Islamic Revolution, which is marked by 10 days of celebrations in early February.