Limited activity on social media suggested unrest in provincial towns was also down.

The United States said it may look to impose fresh sanctions on Iran over its "crackdown", but Russia warned it against interfering in the Islamic republic's internal affairs.

Iranian state TV showed huge crowds marching in support of the government across 10 cities, including Isfahan, Ardebil and Mashhad, where the protests first erupted a week ago.

"We are together behind the leader," chanted the demonstrators, in reference to supreme leader Ayatollah Ali Khamenei.

In a bid to address grievances that drove the initial unrest, Iranian authorities were weighing options including blocking unpopular measures in President Hassan Rouhani's recent budget.

"The people's main demand now is for the government and officials to deal with the economic problems," Ali Akbar Velayati, an adviser to Khamenei, told the semi-official ISNA news agency.

- 'Grotesque intervention' -

The unrest caused international concern, with the United States accusing the authorities of a crackdown on dissent.

A State Department spokeswoman said Thursday that those killed and detained "will not be forgotten", after the White House warned it could impose sanctions on any officials it holds responsible.

US President Donald Trump has repeatedly tweeted his backing for the protesters, his most recent saying he has "such respect for the people of Iran as they try to take back their corrupt government".

Iranian Foreign Minister Mohammad Javad Zarif tweeted back on Thursday: "Trump has an odd way of showing 'such respect'".

"From labelling them a 'terrorist nation' and banning them from visiting the US, to petty insults on the name of the Persian Gulf," he wrote, referring to Trump's use of the term "Arabian Gulf".

Russia jumped to Iran's defence, with deputy foreign minister Sergei Ryabkov telling state agency TASS: "Despite the many attempts to distort what is really going on (in Iran), I am sure that our neighbour, our friend, will overcome its current difficulties."

The question now is whether Trump will continue to waive nuclear-related sanctions suspended under the 2015 nuclear deal between Iran and world powers.

Online messaging and photo sharing platforms Telegram and Instagram remained blocked on mobile phones, having been interrupted soon after protests began.

Telecoms Minister Mohammad-Javad Azari Jahromi said Telegram would only be unblocked if it removed "terrorist" content.

- Parliament responds -

There have already been moves in parliament to block the unpopular budget measures announced last month, which included cuts to welfare and fuel price hikes.

Rouhani came to power in 2013 promising to mend the economy and ease social tensions, but high living costs and unemployment have left many feeling that progress is too slow.

Rural areas, which have seen years of drought and under-investment, are particularly hard-hit.

In the capital, there is widespread sympathy with the economic discontent fuelling the unrest, particularly an unemployment rate that is officially close to 30 percent for young people.

"If the people of Iran have something to say, it's about economic problems. They want to see their demands, what they voted for, fulfilled."