Iran's supreme leader has blamed external "enemies" for heightening turmoil in the country, as the death toll in ongoing nationwide anti-government rallies has passed 20.

The comments by Ayatollah Ali Khamenei, Iran's top authority, came on Tuesday hours before the US said that it would seek emergency United Nations talks on the protests in the Islamic republic.

At least eight people were killed on Monday night, according to state media, taking the number of people killed since the demonstrations began on December 28 to at least 22.

In his first public remarks since the rallies began, Khamenei said that "enemies" of Iran have allied and used the various means they have available, including "money, weapons, politics, and intelligence services", to stir unrest.

"The dignity, security, and progress of the Iranian nation are owed to the self-sacrifice of the martyrs. What prevents enemies from exerting their atrocities is the spirit of courage, sacrifice, and faith within the nation," he said in a statement posted on his official website.

"I have something to say on these events, and I will speak to the dear people when the time is right.

"The Iranian nation will forever owe the dear martyrs, who left behind their homes and families, to stand against the wicked enemies."

US President Donald Trump, who has used Twitter to criticise Tehran since the rallies erupted, hailed the protesters for acting against the "brutal and corrupt" regime and said Iranians had "little food, big inflation and no human rights".

Iran's foreign ministry hit back, saying the US president was "wasting his time sending useless and insulting tweets" and would be better off focusing on "homeless and hungry people" in his own country.

Later on Tuesday, Nikki Haley, Trump's ambassador to the UN, said the US would seek an emergency session of the UN Security Council and the Human Rights Council to discuss Iran.

"The people of Iran are crying out for freedom," she told reporters. "All freedom-loving people must stand with their cause."

'Most politicised rallies in years'

The anti-government rallies first erupted in the second-largest city in Iran, Mashhad, prompted by anger over the high cost of living, rising unemployment and the overall state of the economy under the government of President Hassan Rouhani.

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They quickly spread to other parts of Iran and turned political, with some protesters chanting slogans against Iran's foreign policy, as well as against Khamenei and Rouhani.

Despite threats by the Iranian Revolutionary Guard Corps (IRGC) to put down the demonstrations, protesters have continued taking to the streets, in what has been described as the biggest show of dissent in the country since huge rallies took place in 2009.

So far, at least 530 people - 450 in Iran's capital, Tehran, and 80 in the central city of Arak - have been arrested, according to state media.

Ali Fathollah-Nejad, a visiting fellow at Brookings Doha Center, said the past week's rallies "are the most politicised demonstrations we've had in Iran for a very long time.

"Clearly, the slogans are anti-regime and they target all factions of the Islamic Republic [of Iran], all factions of the establishment," he added, noting, however, that "regime change is such a loaded term because it was misused by a lot of imperialist projects in the past".

Commenting on the allegations that outside actors were stirring unrest, Fathollah-Nejad said that while there is "no doubt" that there are "some external forces who are instrumentalising" what is currently taking place in the country, it must also be acknowledged that these powers "don't have enough influence in Iran anyway.

"The claim by the government to say that a lot of those protests are instigated by the outside, when in the past the same government would say that those forces don't have a following, for example, inside Iran, is just ironic," he told Al Jazeera.

"There are a lot of different interests that are whirling around Iran, but at the same time those protests are somehow organic," added Fathollah-Nejad, noting that the rallies are a backlash against Iran's deeply rooted problems.

"The truth of the matter lies not within the outside world, or with outside forces, but with the very real structural problems that Iranian people have felt over the last few years."

Structural and contingent factors

In May 2017, Rouhani, who belongs to the reformist bloc of Iran's political spectrum, decisively won re-election after garnering 57 percent of the vote in the country's presidential election.

That poll was the first since Rouhani negotiated an historic deal with world powers in 2015, to curb Iran's nuclear programme in exchange for sanctions relief.

Many in Iran hoped that the deal, by lifting many international sanctions, would ease the country's financial struggles.

Yet, the benefits do not seem to have trickled down, with critics blaming the ruling religious elite for economic mismanagement and alleged corruption.

Last month's budget, which included cuts to vital social welfare programmes while giving more money to religious and revolutionary institutions, exacerbated tensions, according to analysts.

"If you have been objectively following the socioeconomic indicators in Iran, you'll see a huge portion of the population has not been benefitting from neither the reformist policies, nor from the conservative ones," said Fathollah-Nejad.

"If you take all those structural factors, plus the more recent contingent factors - the government's response to the [December] earthquakes, student and labour protests, and the budget announcement ... you cannot be very much surprised."