Iran's most powerful man attempted Friday to end seven days of upheaval by warning protesters that they will be held responsible for "bloodshed and chaos" if mass demonstrations continue -- comments which drew swift global condemnation.

Supreme Leader Ayatollah Ali Khamenei said that Mahmoud Ahmadinejad's re-election as president was an "absolute victory" and he warned that protesters would suffer the consequences of their public protests.

In a rare speech at Friday prayers, Khamenei said the results show Ahmadinejad had a landslide victory over pro-reformist Mir Hossein Mousavi.

"If the difference was 100,000 or 500,000 or 1 million, well, one may say fraud could have happened. But how can one rig 11 million votes?" Khamenei asked.

However, anti-government protests continued as night fell in Tehran, with pro-reformers taking to city roofs to yell "Death to the dictator!" and "God is great."

Responding to Khamenei's speech, U.S. President Barack Obama expressed concern about the "tenor and tone" of the statements

Obama's comments come as Washington passed a resolution Friday to condemn Tehran's repressive response to the demonstrations, which erupted a week ago after a highly contested election

The U.S. government drew particular attention to the violence of the crackdown in addition to the suppression of cellphone and Internet use.

Since the results of last week's vote were announced, hundreds of thousands of Iranians have protested against the government saying the election was fixed.

"Protesters had no plans for today, they're going to have their major rally tomorrow afternoon," Nazila Fathi, with The New York Times, told CTV News Channel Friday from Tehran.

Khamenei said elections must be determined at the ballot box, not in the streets.

"I call on all to put an end to this method. ... If they don't, they will be held responsible for the chaos and the consequences," he said.

The demonstrations pose the greatest challenge to the government in 30 years, since the 1979 Islamic Revolution.

However, Khamenei downplayed the actions of the protesters.

"Some may imagine that street action will create political leverage against the system and force the authorities to give in to threats. No, this is wrong," he said.

Meanwhile, George McLeod, a freelance reporter for the Globe and Mail in Iran, said the government is removing most of the remaining reporters in the country.

McLeod said it's too early to determine how the protesters will respond to Khamenei's calls that they stop demonstrating.

Hamid Dabashi, a professor at Columbia University, said Khamenei also took a paternal tone towards the demonstrators Friday telling them not to be manipulated by foreigners.

In response, Britain's Foreign Office said Friday that Iran's ambassador to London has been called to explain Khamenei's comments.

In the U.S., the House of Representatives voted 405-1 Friday to condemn Iran's crackdown on demonstrators and its interference with Internet and cellphone communications.

Rep. Howard Berman, chairman of the House Foreign Affairs Committee and co-sponsor of the resolution, said "it is not for us to decide who should run Iran, much less determine the real winner of the June 12 election."

"But we must reaffirm our strong belief that the Iranian people have a fundamental right to express their views about the future of their country freely and without intimidation," added Berman, a Democrat.

Rep. Ron Paul, a Texas libertarian who is against government meddling, was the sole opposing vote.

With files from The Associated Press