Demonstrators in Tehran marked the 31st anniversary of the Islamic Revolution today with both pro-government and opposition supporters taking to the streets, and President Mahmoud Ahmadinejad declaring Iran a "nuclear state."
A stand-off between the two camps was expected. "It looks like this is going to be a very bloody day," a source in Tehran said.
Iranian state television pictures showed thousands of people holding flags and pictures of the late Grand Ayatollah Khomeini at a rally being addressed by Ahmadinejad.
In his customary fiery rhetoric, Ahmadinejad said that his county was now a nuclear state and vowed not to give in to bullying by the West.
"I want to announce with a loud voice here that the first package of 20 percent fuel was produced and provided to the scientists," he said.
The announcement came days after Iran told the international community of its intention to increase its uranium enrichment to 20 percent from 3.5 percent.
The move brings Iran one step closer to having 95 percent enriched uranium, officially classified as weapons-grade. Iran denies having intentions of building a nuclear bomb, and says it wants the higher-grade material for use at the Tehran Research Reactor, which serves for cancer and other medical treatments.
The international community reacted by starting the process to impose new sanctions on Iran, targeting Iran's Revolutionary Guards and its substantial business interests.
"We are going to be looking at a variety of ways in which countries indicate to Iran that their approach is unacceptable," President Obama said Wednesday. "And the U.N. will be one aspect of that broader effort."
Ahmadinejad said today, "We told them the Iranian nation will never give in to bullying and illogical remarks."
Meanwhile, in other parts of the capital, police and pro-government militia have attacked opposition supporters, most notably Mehdi Karroubi's entourage.
The opposition leader was on his way to join protesters in Sadeghieh Square, downtown Tehran, where many of his supporters had gathered when the Basij, pro-Ahmadinejad militia, mobbed him.
"They all attacked the car and started beating everyone," his son, Hossein Karroubi, said, adding that his father was attacked as soon as he got out of his car and his brother arrested.
"About 100 plainclothes thugs, as well as special police units on motorcycles, attacked the crowd around him with machetes, batons and paint pellets to mark them," Karroubi said.
Ayatollah Khomeini's Granddaughter Detained
An opposition Web site, Rahesabz, reported that the granddaughter of Khomeini, the architect of the Islamic revolution being celebrated today, had herself been detained by security forces.
It was one of the most high-profile detentions in the crackdown by authorities. The granddaughter, Zahra Eshraghi, and husband Mohammad Reza Khatami, who is the brother of a former pro-reform president, were held for about an hour before being released, the Web site said.
Despite the government's fierce crackdown opposition supporters say they remain undeterred.
"People are very, very determined," Mehdi Saharkhiz, an opposition supporter based in the United States, said, adding that many people from across Iran were flocking to the capital to show their support for the opposition.
"All energies are focused on today," Saharkhiz, whose father, an adviser to Karroubi, is in jail.
Protesters, once again, filled the rooftops of Tehran Wednesday night chanting, "Allahu Akbar" ("God is greatest").
"They are loud and coming from everywhere," an observer who requested anonymity said. "It's been many weeks since this has happened."
The chants were first heard before the 1979 revolution, as people called out against the regime of the late Mohammad-Reza Shah Pahlavi. The custom was renewed last summer after the contested elections.
The opposition claims that Ahmadinejad's victory in the June 12 election was fraudulent and that the true winner was opposition leader Mir Hossein Mousavi. Hundreds of thousands marched in the streets against the government in the weeks after the vote, prompting a massive wave of arrests.
Nevertheless, the opposition has succeeded in continuing to hold regular protests, often timing them to coincide with days of important political or religious significance in attempts to embarrass authorities. The tone of the rallies has shifted from outrage about alleged fraud in Ahmadinejad's re-election to wider calls against the entire Islamic system, including Khamenei.
Tensions have mounted further since the last large-scale marches, in late December, which brought the most violent battles with security riots in months. At least eight people were killed in clashes between protesters and police, and security forces have intensified arrests in the weeks since.
Jim Sciutto, Lara Setrakian and The Associated Press contributed to this report.