At least 143 demonstrators were killed across Iran, almost all of them shot by security forces, Amnesty said Monday, as government supporters poured into central Tehran to condemn days of "rioting" that the Islamic republic blamed on its foreign foes.

"According to credible reports... those killed include at least 143 people," Amnesty International said.

"The deaths have resulted almost entirely from the use of firearms," apart from a death from tear gas and another after a beating, it added.

Amnesty, which last week gave a death toll of more than 100 as security forces stamped out protests that followed fuel price rises on November 15, said it believed the actual toll would climb "significantly higher" as it investigated.

The London-based watchdog called for world powers to condemn the bloodshed.

"The international community's cautious and muted response to the unlawful killing of protesters is woefully inadequate," said Philip Luther, Amnesty's research and advocacy head for the Middle East.

140+ Iranian protesters have been killed in 5 days. Iranian security forces shot unarmed people on streets, from rooftops & a helicopter. 1,000+ protesters have been arrested. The internet was blocked to stop the world from seeing this. Watch what's been happening in #Iran. pic.twitter.com/CjA4VnnGY0

— Amnesty International (@amnesty) November 25, 2019

Amnesty said "verified videos show security forces deliberately shooting unarmed protesters from a short distance. In some cases, protesters were shot while they were running away".

They also showed security forces shooting from rooftops, it said, adding that the crackdown was carried out by police, Revolutionary Guards, and the Basij paramilitary force "and others".

In central Tehran on Monday, supporters of Iran's government filled Enghelab (Revolution) Square Tehran for a massive rally.

Waving the Iranian flag and banners that read "Death to America", government supporters descended on the square from all directions.

Internet outage

Connectivity has returned to much of the country except for its mobile telephone networks, said NetBlocks, a site that monitors internet disruptions.

The unrest erupted hours after a midnight announcement that the price of petrol would be immediately raised by 50 percent for the first 60 litres and 200 percent for any extra fuel after that each month.

Iran's President Hassan Rouhani said the proceeds would allow his government to provide welfare payments to the needy.

During the violence, dozens of banks, petrol pumps and police stations were torched across Iran.

Officials have confirmed five people were killed, despite the toll from Amnesty and UN fears that dozens had died.

Authorities say they arrested 180 ringleaders.

The total number of people detained remains unclear, but the UN human rights office put it at more than 1,000 last Tuesday.