Iran's judiciary said it will "firmly punish" women who violate strict dress rules, as the United Nations warned Tehran is trying to crush protests by weaponising the death penalty.

Demonstrations have swept Iran since the 16 September death of Iranian Kurdish woman Mahsa Amini, 22, after her arrest in Tehran for allegedly failing to adhere to the dress rules which demand women wear hijab headscarves.

After nearly four months of protests, in which Iran has hanged four people for their role in the unrest, the UN Human Rights Office in Geneva said Iran's executions without due process amount to "state-sanctioned killing".

Since the outbreak of the protests, the morality police units charged with enforcing the hijab rules have been less visible and many women have taken to the streets with their heads uncovered.

But as the demonstrations continue, the prosecutor general on Tuesday issued a directive in which "police were ordered to firmly punish any hijab violations", Mehr news agency reported.

"Courts must sentence the violators, as well as fine them, to additional penalties such as exile, bans on practising certain professions and closing workplaces," Mehr quoted the judiciary as saying.

Read More:
Iran sentences 3 more to death over Amini protests
EU 'appalled' by new protester executions in Iran
Outrage as Iran carries out first execution over Amini protests

Iran's judiciary said it had sentenced another man to death in connection with the protests, with Javad Rouhi found guilty of charges of "corruption on Earth".

Mr Rouhi was found guilty of "leading a group of rioters", "inciting people to create insecurity", as well as of "apostasy by desecration of the Koran by burning it", the judiciary's Mizan Online news website reported.

The sentence, which can still be appealed, brings to 18 the total number of people the judiciary have announced have been condemned to death in connection with the protests.

Of those 18 confirmed, four are already dead and six face retrials.

However, Oslo-based group Iran Human Rights (IHR) says at least 109 protesters now in detention have been sentenced to death or face charges that can carry capital punishment.

Iran has blamed the unrest on hostile foreign forces, and supreme leader Ayatollah Ali Khamenei said Monday that authorities had been dealing "seriously and justly" with those implicated in the "riots".

In an updated death toll, IHR said Monday that 481 protesters had been killed, including 64 minors, since the unrest began.

Iranian authorities say hundreds, including members of the security forces, have been killed.

'Strike fear'

The UN warned that Iran is using capital punishment to frighten the public and crush dissent.

"Criminal proceedings and the death penalty are being weaponised by the Iranian government to punish individuals participating in protests and to strike fear into the population so as to stamp out dissent, in violation of international human rights law," UN rights chief Volker Turk's office said.

"The weaponisation of criminal procedures to punish people for exercising their basic rights -- such as those participating in or organising demonstrations -- amounts to state-sanctioned killing," Turk added.

The crackdown and executions have sparked global outrage and fresh Western sanctions against Tehran.

Rights groups have also accused Iran of extracting forced confessions and denying the thousands arrested due legal process.

According to London-based rights group Amnesty International, Iran is second only to China in its use of the death penalty, with at least 314 people executed in 2021.