Iran's supreme leader Ayatollah Ali Khamenei said on Wednesday that his country will "never surrender" in the face of threats by US President Donald Trump to join Israel's war in the air.

In a televised speech a day after Mr Trump hinted he could have Iran's leader assassinated, Mr Khamenei said any US involvement in Israel's war would have “irreparable” consequences.

Mr Trump said his patience with Iran had "run out ", as he continued to send mixed signals on whether the US will join the Israeli attacks on Iran. Asked whether it was too late for negotiations, he said: "Nothing is too late."

Israel and Iran exchanged a sixth day of fire with no peace talks in sight. The Israeli military said it hit Tehran, where explosions were heard, while fighter jets attacked alleged missile storage sites in western Iran. Israeli Defence Minister Israel Katz said an Iranian internal security headquarters had been destroyed.

Air raid sirens in the Golan Heights signalled Iran's response with a drone attack that Israel said it had intercepted. Tehran said its air defences had shot down 28 aerial vehicles, including a spy drone, in 24 hours.

Iran on Wednesday denied sending a delegation to Oman for negotiations on a ceasefire with Israel. Reports claimed three Iranian planes were on their way to Muscat for talks with US officials, but Iranian foreign ministry spokesman Esmail Baghaei said that "such news is not accurate".

The UN's nuclear watchdog said a workshop and research centre used to produce centrifuges for uranium enrichment were attacked. Israel says Iran is developing nuclear weapons, which Mr Trump says must never be allowed to succeed.

“The US President threatens us,” Mr Khamenei said. “With his absurd rhetoric, he demands that the Iranian people surrender to him. They should make threats against those who are afraid of being threatened. The Iranian nation isn’t frightened by such threats.

“It isn’t wise to tell the Iranian nation to surrender. What should the Iranian nation surrender to? We will never surrender in response to the attacks of anyone. This is the logic of the Iranian nation. This is the spirit of the Iranian nation.”

Tehran had threatened to attack US military bases in the Middle East if the US entered the war.

“The US entering this matter [war] is 100 per cent to its own detriment,” said Mr Khamenei. “The damage it will suffer will be far greater than any harm that Iran may encounter. The harm the US will suffer will definitely be irreparable if they enter this conflict militarily.”

The supreme leader was responding after Mr Trump demanded Tehran's “unconditional surrender” and said America's patience is wearing thin, apparently paving the way for the US to join Israel’s war against Iran.

Explained: How US involvement could affect Israel-Iran war

01:48

In two posts on Truth Social on Tuesday, Mr Trump warned Mr Khamenei that the US knows where he is “hiding” but does not plan to kill him, “at least for now”. In a subsequent post, he wrote simply: “Unconditional surrender!”

Mr Trump had earlier said “we” have control of the skies above Iran, and hailed the use of US-made weapons. His remarks came after he urged Tehran's residents to evacuate the Iranian capital. Residents poured out of the city, and shops and the historic Grand Bazaar were closed on Tuesday.

Several countries began evacuating their citizens from Iran and Israel as flights are scrapped and airspaces closed due to the air war. Some Europeans leaving Israel were taken by bus to Jordan or Egypt before flying home.

China has evacuated nearly 800 citizens and has started moving its citizens from Tehran to Turkmenistan by bus, a distance of 1,150km, the state-run China News Service reported.

Israel began bringing stranded citizens home on special flights to Ben Gurion Airport, which remained closed to commercial traffic. A first plane load arrived from Cyprus on Wednesday in what Israel is calling Operation Safe Return.

On the home front, the Israeli military eased some restrictions on residents. While schools remain closed, gatherings of up to 30 people can take place and workplaces reopen if a bomb shelter can be reached within a certain time.

Must be punished

Mr Trump flew back to Washington late on Monday, cutting short his trip to the G7 summit in Canada to confer with his national security team as the Israel-Iran air war raged for a fifth day.

His comments were a far cry from earlier messages, in which he maintained that a US-Iranian nuclear deal remained within reach.

In his second revised message since the war started on Friday, the Iranian leader praised the “firm and courageous stance of the Iranian nation” in the face of the Israeli attacks.

He stressed that the Iranian nation “firmly stands against any imposed peace. The Iranian nation will not capitulate to anyone in the face of coercion”.

Israeli strikes have hit several nuclear and military sites, killing senior generals, nuclear scientists and hundreds of civilians.

Trump urges Tehran's 'unconditional surrender' as US edges closer to war with Iran

01:37

Iran has fired about 400 missiles and hundreds of drones in retaliatory strikes that have killed at least 20 people in Israel and wounded hundreds. Some have hit apartment buildings in central Israel, causing heavy damage, and air raid sirens have repeatedly forced Israelis to run for shelter.

Iran has fired fewer missiles as the conflict has worn on. It has not explained the decline, but Israel has targeted launchers and other infrastructure related to the missiles.

Mr Khamenei acknowledged that “there was no indication on the part of Iran that signalled a military move”, as the Israeli attack took place at a time when Iranian officials were engaged in negotiations with the US.

“It was already suspected that the US was involved in the malicious move carried out by the Zionist regime, but considering their recent remarks, this suspicion is growing stronger day by day,” he added.

“The Zionist enemy has made a grave mistake and committed a serious crime, and it must be punished.”