Tehran, Iran (CNN) Iran's Supreme Leader Ayatollah Ali Khamenei led Friday prayers in Tehran for the first time in eight years, amid public fury over the military's shooting down of a passenger jet and sky-high tensions with the US.

Khamenei mocked US officials as "American clowns" and criticized France, Germany and the UK as "lackeys" of the US that can't be trusted. He also expressed his condolences to the families of victims of the plane crash.

It is rare for Khamenei -- the highest spiritual and political authority in Iran -- to lead Friday prayers, and the move is thought to be an effort to rally support after several tumultuous weeks that have piled pressure on the Islamic Republic's rulers.

Iran's most important general, Qasem Soleimani, was killed in a US drone strike in Iraq two weeks ago, and Iran retaliated with strikes on US targets, bringing Tehran and Washington briefly to the brink of all-out conflict.

Iran's military then shot down a Ukrainian commercial flight in Tehran, killing all 176 people onboard, including 82 Iranians, prompting days of protests and finger-pointing between rival factions of the government.

In a defiant sermon Friday, Khamenei described the "martyrdom" of Soleimani and Tehran's retaliation against the US as "acts of God, not man," and boasted that Iran had delivered a slap in the face to the United States.

"What took place could not have been the work of any human actor, only the hand of God," Khamenei said. "The day in which the missiles of [Iran's Revolutionary Guards] rained down upon the American base, that was also the day of the Almighty."

"We saw history in the making. These are not normal days. The fact that a power, a nation, does possess the spiritual strengths in order to respond to the biggest bullying power in the world with such a slap in the face, this shows the divine hand, the hand of God", the Supreme Leader said.

Khamenei also railed against US President Donald Trump and Secretary of State Mike Pompeo, who have said on social media that they stand with Iranian protesters.

He said "American clowns" lie to the public when they say the US is with the people of Iran.

"If you stand in close proximity to Iran, it is with the intention of driving a knife into the chest of the people," he said.

Khamenei added Iran is open to negotiations, but not with the United States. "We have no fear of negotiations," he said, "but of course not with America."

The leader said his country would only negotiate with others "from a position of strength," not "weakness." He did not provide any details about which countries Iran was open to negotiating with when he said "others."

Huge crowds were present to witness the rare sermon, with President Hassan Rouhani in the front row alongside parliament speaker Ali Larijani. The last time Khamenei presided over Friday prayers was in 2012 to mark the 33rd anniversary of the Islamic Revolution. He also led prayers in 2009 amid protests that erupted after disputed presidential elections.

Over the past few days Iranian radio broadcasts and television had been encouraging people to join the prayers.

They come at a pivotal time for Iran, after vigils to mourn those who died in the Ukraine International Airlines crash quickly turned into mass anti-government demonstrations, with calls for Khamenei to step down and for those responsible for downing the plane to be prosecuted.

Iran's military initially denied shooting down the plane before admitting to it several days later, saying the plane was "accidentally hit by human error."

Khamenei expressed his condolences to the families of the victims, but said foreign press had tried to deceive Iranians over the crash.

"Our enemy tried to manipulate the bitter crash of the plane to overshadow our accomplishments," he said.

"The events that followed the crash must not be allowed to repeat themselves," Khamenei added, which could be taken as a stern warning to security forces not to allow further protests or unrest.

Foreign Minister Mohammed Javad Zarif said earlier this week that people had taken to the streets because they were "lied to for a couple days."

Khamenei also addressed ongoing tension with France, Germany and the UK -- the so-called E3 nations -- who triggered a dispute mechanism in the Iran nuclear deal that could lead to a further unraveling of the accord.

"Today it has been clear that these European countries are the lackeys and yes men of America," he said.

"But, you the European countries must bear in mind the America has not managed to bring the Iranian nation down to its knees, let alone you, you are much less mighty than America."

The Europeans are "an iron fist that has been given the veil of a velvet glove," said Khamenei. "They cannot be the people who we trust."