US President Donald Trump has warned Iran's authorities against killing peaceful protesters, saying Washington "will come to their rescue".

In a brief post on social media, he wrote: "We are locked and loaded and ready to go." He gave no further details.

A senior adviser to Iran's Supreme Leader, Ayatollah Ali Khamenei, responded by saying Trump should "be careful" if he intervened, warning of potential chaos across the Middle East.

At least six people are reported to have been killed in Iran on Thursday after almost a week of mass protests sparked by worsening economic conditions.

In Friday's post on Truth Social, Trump wrote: "If Iran shots [sic] and violently kills peaceful protesters, which is their custom, the United States of America will come to their rescue."

Khamenei adviser Ali Larijani warned shortly afterwards that any US interference would destabilise the region.

"Trump should know that US interference in this internal matter would mean destabilising the entire region and destroying America's interests," he wrote.

In his post, the US president did not specify what action Washington could take against the Iranian authorities.

In June, the US carried out strikes against Iran's nuclear sites on Trump's orders.

American officials later argued that the strikes had significantly set back the prospect of Tehran building a nuclear weapon - a claim disputed by Iran.

In retaliation, Iran launched a missile attack on a major US military base in Qatar.

In Iran, six people were reported to have been killed on a fifth day of protests on Thursday.

Footage filed by Reuters shows protests in Iran's Lorestan province outside a police station

Two people died in clashes between protesters and security forces in the south-western city of Lordegan, according to the semi-official Fars news agency and the human rights group Hengaw.

Three people were killed in Azna and another in Kouhdasht, all in the west of the country, Fars reports.

Fars did not specify whether those killed were demonstrators or members of the security forces.

Hengaw said the two killed in Lordegan were protesters, naming them as Ahmad Jalil and Sajjad Valamanesh.

BBC has not been able to independently verify the deaths.

Footage posted on social media showed cars set on fire during running battles between protesters and security forces.

BBC Persian has verified videos showing Thursday's protests in Lordegan, Tehran and Marvdasht in the southern Fars province.

Iranian officials earlier said a member of the country's securities forces had been killed on Wednesday in the western city of Kouhdasht. The BBC has not been able to verify this and protesters say the man was one of their number and was shot dead by the security forces.

The protests began on Sunday in Tehran among shopkeepers angered by another sharp fall in the value of the Iranian currency, the rial, against the US dollar on the open market.

By Tuesday, university students were involved and they had spread to several cities, with people chanting against the country's clerical rulers.

Many protesters have since been calling for the end of Khamenei's rule. Some have said they want a return to the monarchy.

The protests have been the most widespread since an uprising in 2022 sparked by the death in custody of Mahsa Amini, a young woman accused by morality police of not wearing her veil properly, but they have not been on the same scale.

President Masoud Pezeshkian has said he will listen to the "legitimate demands" of the protesters.

But the country's Prosecutor-General, Mohammad Movahedi-Azad, warned that any attempt to create instability would be met with a "decisive response".