Iran faced the prospect of an international investigation Thursday as the U.N. rights chief Volker Türk urged the country to immediately halt its violent crackdown on protesters.

Türk opened an emergency session of the U.N. Human Rights Council, where countries were called to discuss Iran's "deteriorating human rights situation" and determine if a high-level international investigation is warranted.

The meeting, requested by Germany and Iceland with the backing of more than 50 countries, follows two months of protests in Iran sparked by the death of 22-year-old Mahsa Amini, after she was arrested for an alleged breach of the country's strict dress rules for women based on Islamic sharia law.

"I call on the authorities immediately to stop using violence and harassment against peaceful protesters," said Türk, the United Nations' high commissioner for human rights.

"The unnecessary and disproportionate use of force must come to an end," he said, warning that Iran was in "a full-fledged human rights crisis."

"Accountability is a key ingredient of the pursuit of justice for human rights violations," he told the 47-member council, urging the body to vote in favour of an investigation.

Iranian authorities have grown increasingly heavy-handed in their response, as the demonstrations have spread across the country and swelled into a broad movement against the theocracy that has ruled Iran since 1979.

Türk said more than 300 people had been killed since Amini's death. Norway-based group Iran Human Rights has put the toll above 400, including more than 50 children.

"The security forces ... have used live ammunition, birdshot and other metal pellets, tear gas and batons," said Türk.

He also said around 14,000 people, including children, have been arrested in the context of the protests, describing this as "a staggering number."

At least six people have so far been sentenced to death in connection with the protests.

No 'moral credibility'

In its reaction, Tehran slammed the Western countries that called for the urgent session, saying they lacked "moral credibility."

The United States and European countries who pushed for Thursday's meeting "lack the moral credibility to preach others on human rights and to request a special session on Iran," Iran's deputy of the vice president for women and family affairs, Khadijeh Karimi, told the council in Geneva.

Germany and Iceland, however, received broad backing for their request to hold Thursday's session, including from more than a third of the council's 47 members.

Western diplomats voiced cautious optimism that the resolution would go through but acknowledged it could be tight.

50 police killed

Also on Thursday, Iranian authorities said around 50 police have been killed in the protests so far since September.

"Around 50 police officers were killed during the protests and hundreds were injured," said Iran's deputy foreign minister, Ali Bagheri Kani, who is also Iran's chief nuclear negotiator, in an interview on Indian television.

He gave no figure for the number of protesters killed but said the Interior Ministry had formed a panel to investigate the deaths. Iranian state media reported last month that 46 security forces had been killed but without citing officials.