Iranian security forces arrested some 3,700 people during widespread protests and unrest over the past two weeks, a lawmaker said Tuesday, offering a far higher number than authorities previously released.

The demonstrations, which began Dec. 28 over economic grievances, quickly spread across the country to become the largest seen in Iran since the disputed 2009 presidential election. Some protesters called for the overthrow of the government, and at least 21 people were killed in clashes.

Human rights activists outside of Iran told The Associated Press they weren't surprised by the figure as authorities also allegedly carried out so-called "preventative arrests" of students not involved in the protests. Some 4,000 arrests followed the 2009 protests.

Activists also said they had concerns about Iran's prisons and jails being overcrowded and dangerous, pointing to allegations of torture, abuse and deaths that followed the mass arrests of 2009. The New York-based Center for Human Rights in Iran says at least three detainees arrested in the recent protests have already died in custody.

"Given the systematic rape and torture of detainees in 2009 in very overcrowded and inhumane conditions, we are extremely worried about the fate of these thousands of detainees and the lack of information and access by their families and lawyers," said Hadi Ghaemi, the executive director of the center. "It is a very troubling situation."

Mahmoud Sadeghi, a reformist lawmaker from Tehran, offered the new figures for those arrested in a report carried Tuesday by parliament's official news website. Authorities previously spoke of hundreds of arrests in Tehran, while other provinces offered only piecemeal figures, if any at all.

Sadeghi said 3,700 was the best number he could immediately offer, given that various security forces around the country had been involved in the arrests. Iran put more police on the streets over the arrest, including anti-riot squads, while the paramilitary Revolutionary Guard also deployed its motorcycle-riding Basij volunteer force.

Sadeghi did not elaborate, nor did he say how he came up with the figure. While reformists largely stayed away from the recent protests, releasing such figures puts pressure on their hard-line opponents who exercise control over Iran's judiciary and security services.

Interior Minister Abdolreza Rahmani Fazli previously said about 42,000 people at most took part in the anti-government protests. Sadeghi's figure of arrested offered Tuesday would mean nearly 10 percent of those who demonstrated were arrested.

On Tuesday, authorities in Tehran released another 70 prisoners on bail after releasing an earlier batch of 70 on Sunday, Tehran prosecutor Abbas Jafari Dolatabadi said, according to the semi-official ISNA news agency.

Iranian authorities have said that the protests are waning. That's in part due to the government blocking access to the popular messaging app Telegram, which demonstrators used to share images of the rallies and organize. It remains difficult for journalists and outsiders to piece together what's happening beyond Tehran, as Iran is a vast country of 80 million and travel is restricted.

Government supporters have also held several mass rallies across Iran to protest the unrest.

Similar mass arrests followed the Green Movement protests over voter fraud allegations in the 2009 re-election of President Mahmoud Ahmadinejad, a crackdown that saw dozens killed and others tortured in custody. Rape accusations levied against jailers at the time stunned Iran.

In these protests, the Center for Human Rights in Iran said it had documented the deaths of three detainees. One died at Tehran's Evin prison in a reported suicide. Another man detained in Arak, 150 miles southwest of Tehran, also reportedly died in a suicide, though his family said their son's body bore an enormous head wound "as if he had been hit with an ax," the center said.

The center alleges a third detainee died in custody in Dezful, 285 miles southwest of Tehran. While Iranian media has quoted a lawmaker on the Evin prison death, the other two had not been reported as of Tuesday.

Some university students separately have been arrested even though they haven't taken part in the demonstrations, said Nassim Papayianni, a London-based researcher on Iran for Amnesty International. She said authorities have described those arrests as "preventative."

The mass arrests raise questions about those detained receiving legal assistance and proper care while in custody, she said.

"We already know that many of these prisons before these arrests were overcrowded," Papayianni said. "We know that people would sleep on floors in the winter.... There wouldn't be even sufficient food."

US officials and analysts studying Iran believe conservative opponents of President Hassan Rouhani, a relative moderate within Iran's clerically overseen government, started the demonstrations but quickly lost control of them.

Iran's Supreme Leader Ayatollah Ali Khamenei on Tuesday also blamed "Americans and Zionists" for the protests, saying money supporting them came from "one of the filthy-rich governments of the Persian Gulf."

Mr. Khamenei, however, also stressed that those with legitimate complaints about Iran's economy should be heard.

Get the Monitor Stories you care about delivered to your inbox. By signing up, you agree to our Privacy Policy

"We should differentiate between people's righteous and honest demands on one side and barbaric and disruptive moves by another group," he said. "These should be distinguished from each other."

This story was reported by The Associated Press.