At least seventeen people were killed in Pakistan on Sunday during protests following the death of Iran's supreme leader, including attempts to storm US diplomatic missions in the country.

In the megacity of Karachi, an AFP journalist saw hundreds of pro-Iranian demonstrators during the day attempting to enter the American consulate before being dispersed by police who notably used tear gas.

At least ten people were killed and the toll was 70 injured on Sunday evening, according to Karachi police.

At least nine people were killed by gunfire, according to hospital records seen by AFP.

Authorities in Sindh province, which includes Karachi, have ordered an investigation, according to a statement.

"We don't need anything in Pakistan that is linked to the United States," said Sabir Hussain, one of the protesters.

The protesters chanted slogans hostile to the United States, Israel, and their allies.

Earlier in the morning, according to videos circulating on social media, protesters had scaled the perimeter wall and broken windows of the American consular building, some declaring their intention to set it on fire, before the police intervened.

In the northern city of Gilgit, at least seven people were killed in clashes with police that also left many injured, a rescue official, Zaheer Shah, told AFP by telephone.

In the capital Islamabad, some 4,000 people demonstrated, brandishing photos of Iranian supreme leader Ali Khamenei, killed the previous day by American and Israeli strikes on Tehran.

AFP journalists heard warning shots aimed at dispersing the crowd, and saw police use tear gas near the US embassy.

- "Lackeys of the United States" -

In Skardu (north), protesters set fire to a United Nations office and three vehicles, and thousands of people demonstrated in Lahore (east).

Pakistani Prime Minister Shehbaz Sharif said on Sunday that the killing of Iran's Supreme Leader, Ayatollah Ali Khamenei, in US-Israeli strikes on Tehran was a "violation" of international law.

"The people of Pakistan join the Iranian people in these hours of pain and sorrow, and offer their sincerest condolences for the martyrdom" of Ali Khamenei, he also said.

But in Islamabad, Zahra Mumtaz, a 52-year-old protester, was outraged that she could not express her anger.

"Our leaders are nothing more than lackeys of the United States," she told AFP.

"The least our government should do is let us express our grief," she added.

The US and UK embassies in Pakistan have urged their citizens to exercise caution.

Pakistani Prime Minister Shehbaz Sharif called for restraint following strikes carried out since Saturday morning by the United States and Israel, which he essentially described as an Israeli operation.