US President Donald Trump has promised Iranians that "help is on the way" as they continue to hold mass protests in cities across the Middle Eastern nation.
The president's comments have set off concerns that he might order military action against Iran.
Whatever course of action Mr Trump decides to take, it will become the latest chapter in his country's storied history with Iran.
From a CIA-led coup to a hostage crisis and air strikes, here are some of the defining moments in seven decades of relations between the US and Iran.
1953: Operation Ajax
Emerging from the ashes of World War II, Iran determined to nationalise the British-owned Anglo-Iranian Oil Company, which operated in the country's vast oil fields.
But when retaliatory sanctions from London saw the collapse of Iran's economy, the US became concerned the Soviet Union could gain influence in the region.
Under president Dwight D Eisenhower, the CIA led a messy coup that overthrew Iran's government and returned to power a monarchy with Western sympathies.
While he may have been the US's choice of leader, Shah Mohammad Reza Pahlavi was considered deeply unpopular in Iran.
He relied on American support to remain in power for the ensuing two decades.
1979: The Iranian Revolution
After months of mounting civil unrest pushing for a revolution, Mohammad Reza Pahlavi became convinced Western nations were now working against him and fled the country on January 16.
In February, Grand Ayatollah Ruhollah Khomeini, a cleric who opposed the westernisation of Iran, returned to the country after 14 years of exile.
He took power as supreme leader in December and shook Iran's ties with the US, transforming the country into an Islamic theocracy, governed according to the principles of religious law.
1979-81: The hostage crisis
On November 4, 1979, a group of Iranian students stormed the US Embassy in Tehran and took 66 American diplomats and civilian personnel hostage, including 52 who were held captive for more than a year.
They demanded the extradition of Mohammad Reza, who had wound up in the US, seeking cancer treatment.
Washington severed ties with Tehran in response and imposed a series of economic sanctions on Iranian exports and assets.
The hostages remained in captivity for 444 days until their release under the Algiers Accords, signed on January 19, 1981 — a day before US president Ronald Reagan took office.
As part of the accords, the US agreed not to intervene in Iranian politics, but relations between the two nations remained poisoned for decades after the incident.
2002: The 'axis of evil'
By the turn of the century, tensions between the US and Middle Eastern countries such as Iraq and Lebanon had intensified.
In his 2002 State of the Union address, US president George W Bush labelled Iran, Iraq and North Korea the "axis of evil".
"By seeking weapons of mass destruction, these regimes pose a grave and growing danger," he said.
"They could provide these arms to terrorists, giving them the means to match their hatred. They could attack our allies or attempt to blackmail the United States.
"In any of these cases, the price of indifference would be catastrophic."
The US-based Council on Foreign Relations think tank reports that Iran and America had established a "back channel" in the wake of the September 11 terrorist attacks on the US that killed about 3,000 people, holding secret meetings to track down operatives of Al Qaeda, which was responsible for 9/11.
The countries also had a shared enemy — the Taliban in Afghanistan.
Later that year, the Iranian opposition claimed the government was secretly developing nuclear facilities, including a uranium enrichment plant.
It sparked fears of a nuclear weapons program — something the US openly accused Iran of pursuing before it imposed a series of economic sanctions on Tehran.
2013-16: Turning the temperature down
During his second term in the White House, US president Barack Obama took steps to ease simmering tensions with Iran.
A month after Iran's new president Hassan Rouhani took office in 2013, the pair spoke on a phone call — which was touted as the first top-level conversation between leaders of the two countries in more than three decades.
Two months later, Iran was ready to negotiate on curbing its nuclear program in exchange for relief from economic sanctions.
Iran, the US, the European Union and other world powers reached a final agreement in 2015: the Joint Comprehensive Plan of Action (JCPOA).
As part of the deal's terms, Iran was required to downscale its nuclear activity — inhibiting its capacity to develop nuclear weapons — and to allow inspections of its facilities.
Mr Rouhani pledged Iran would "never seek a nuclear weapon, with or without the implementation" of the deal.
2018-19: Trump winds back US commitments
The JCPOA's authority suffered a major blow in 2018 when, during his first term as president, Mr Trump withdrew the US from the agreement.
The president claimed the deal had not stopped Iran from developing nuclear weapons and had given the regime "billions of dollars".
He said he wanted to place "maximum pressure" on Iran and reinstated crippling economic sanctions.
Iran was pushed into a deep recession as a result and hit back by ramping up its uranium enrichment efforts.
2020: A leader assassinated
Days after the US Department of Defense accused him of overseeing attacks on US military bases in Iraq, American forces killed Iranian Major General Qassem Soleimani in a drone strike while he was in Baghdad for diplomatic talks.
General Soleimani was the head of Iran's elite Quds Force of the Islamic Revolutionary Guard Corps, which the Trump administration had designated a Foreign Terrorist Organisation in 2019.
He was widely considered to be Iran's second-most-powerful person behind the country's Supreme Leader Ayatollah Ali Khamenei, and was responsible for orchestrating Iran's foreign military actions.
"Soleimani was plotting imminent and sinister attacks on American diplomats and military personnel, but we caught him in the act and terminated him," Mr Trump said in a statement at the time.
"For years, the Islamic Revolutionary Guard Corps and its ruthless Quds Force — under Soleimani's leadership — has targeted, injured, and murdered hundreds of American civilians and servicemen."
The strike escalated demonstrations in Iraq over both Iranian and US influence in the country, and in Iran, where protesters were pushing back on the theocratic regime.
2025: Midnight Hammer and the end of the JCPOA
In an 18-hour stealth operation launched from Missouri on June 21, the US deployed B-2 fighter jets carrying "bunker-busting bombs" that flew across the Atlantic Ocean to attack Iran's Fordow, Natanz and Isfahan nuclear sites.
At the same time as the jets entered Iranian airspace, a US submarine launched more than two dozen Tomahawk missiles against key Iranian infrastructure targets, General Dan Caine said.
US Defense Secretary Pete Hegseth highlighted Israel's role in the operation "in degrading Iranian capabilities, degrading Iranian launchers, MRBMs (medium-range ballistic missiles)" in the lead-up to the strikes.
Mr Trump lauded the operation as a "spectacular military success," claiming it had "completely obliterated" Iran's nuclear capabilities.
It was described as the first time US forces had directly attacked targets on Iranian soil.
In the months that followed, Iran refused to cooperate with requests from the International Atomic Energy Agency to inspect the damaged sites to assess any potentially dangerous nuclear leaks.
The United Kingdom, Germany and France responded to that refusal by triggering a "snapback process" to reinstate United Nations-issued sanctions against Iran.
Days before the JCPOA's "termination day", which was set for October 18 — exactly 10 years after the deal was first adopted — Tehran announced it would end the agreement "including the restrictions on the Iranian nuclear program".
2026: Trump promises 'help is on the way'
Protests exploded across Iran in the final days of 2025 and continue.
Sparked by an economic crisis, the movement quickly broadened into opposing the government.
Desperate to quell the unrest, the government shut down internet and telephone networks.
US-based human rights monitor HRNA says 2,500 people have been killed, but the opposition network Iran International, which is based in London, estimates that toll is as high as 12,000.
Mr Trump traded barbs online with top Iranian officials, vowing a US intervention if peaceful protesters were killed.
The president said on Friday that Iranian authorities "better not start shooting, because we'll start shooting too".
In return, Iranian officials threatened to attack Israel or US military bases in the region.
But Mr Trump has so far not been deterred from a possible intervention.
After reportedly being briefed on possible actions the US could take, he told Iranians to "keep protesting," and that "help is on the way".
