Demonstrators gathered in a number of cities around the world Saturday to call for the release of opposition supporters who were detained during protests against Iran's controversial presidential election.

Groups such as Human Rights Watch and Amnesty International planned the day of protest, which was scheduled to take place in more than 80 cities, including Toronto, Montreal and Vancouver.

The protesters said hundreds, possibly thousands, of Iranians were detained during the demonstrations that rocked Tehran in the days following the election, in which President Mahmoud Ahmadinejad was declared the victor.

Hundreds gathered on the lawns of Queen's Park in Toronto to speak out against the violence in Iran.

"We want to show our support and show the world and especially let the Iranian authorities know that we are here and standing behind our prisoners and we will not stand for any violation of their human rights," protester Faoud Oveisy told CTV Toronto.

Fellow protester Dr. Shaharan Aazam said he's worried about his niece, a 22-year-old student that has been detained in Iran.

"She's not really a political activist, she was just a regular young girl on the street and suddenly she disappeared," he said.

A group of cyclists left from the Queen's Park rally and began a bike trek across the province to the Iranian embassy in Ottawa where they hope to deliver a petition demanding the release of political prisoners.

Worldwide protests

About 600 protesters congregated outside the Iranian embassy in London in a "noisy but peaceful," demonstration, police said.

In Amsterdam, Iranian Nobel Peace Prize laureate Shirin Ebadi urged several hundred demonstrators to call for new elections to be monitored by the United Nations.

Some protesters shouted "Death to the Islamic regime!" However, Ebadi told the demonstrators to call instead for life and democracy.

Another several hundred people turned out for a rally in Paris at Trocadero square, near the Eiffel Tower.

Protesters carried signs that read, "Free Iran" and "Where is my vote?" Others stood behind a cloth banner painted to resemble bars on a jail cell.

"We've had enough of religious regimes that don't have the Iranian people's best interest at heart," protester Sakineh Davoodi, a 50-year-old cashier from Iran who has lived in France for 23 years, told The Associated Press.

More than 80 people, many wearing the green colour of Iran's reformist movement, gathered outside the UN's European headquarters in Geneva.

"The young people have had enough," said protester Jacky Carel, a member of a Swiss-Iranian cultural organization. "It cannot go on like this."

Dozens of demonstrators turned out at similar rallies in cities from Brussels, Belgium, to Islamabad, Pakistan, to Melbourne, Australia.

Hundreds of thousands of Iranians took to the streets following the June election and faced a brutal crackdown by government security forces.

In addition to the arrests, the Iranian government barred journalists from covering the protests.

At least 20 people were killed in the violence.

With files from The Associated Press and a report from CTV Toronto's Michelle Dube