Iran has said its ballistic missile strike targeting Islamic State in Syria was not only a response to deadly attacks in Tehran, but a powerful message to rival Saudi Arabia and the United States.
The launch, which hit Syria's eastern city of Deir el-Zour on Sunday night, appeared to be Iran's first missile attack abroad in more than 15 years and its first in the Syrian conflict, in which it has provided crucial support to embattled president Bashar Assad.
It comes amid the worsening of a long-running feud between Shiite powerhouse Iran and Saudi Arabia, which supports Syrian rebels and has led recent efforts to isolate the Gulf nation of Qatar.
It also raises questions about how US President Donald Trump's administration, which had previously put Iran "on notice" for its ballistic missile tests, will respond.
Iran's powerful Revolutionary Guard, a paramilitary force in charge of the country's missile programme, said it launched six Zolfaghar ballistic missiles from the western provinces of Kermanshah and Kurdistan.
State television footage showed the missiles on truck missile launchers in the daylight before being launched at night.
The missiles flew over Iraq before striking what the Guard called an IS command centre and suicide car bomb operation in Deir el-Zour, more than 600 kilometres (370 miles) away.
The extremists have been trying to fortify their positions in the Syrian city in the face of a US-led coalition onslaught on Raqqa, the group's de facto capital.
Syrian opposition activist Omar Abu Laila, who is based in Germany but closely follows events in his native Deir el-Zour, said two Iranian missiles fell near and inside the eastern town of Mayadeen, an IS stronghold.
He said there were no casualties from the strikes. IS did not immediately acknowledge the strikes.
Iraqi politician Abdul-Bari Zebari said his country agreed to the missile overflight after co-ordination with Iran, Russia and Syria.
The Guard described the missile strike as revenge for attacks on Tehran earlier this month that killed at least 18 people and wounded more than 50, the first such IS assault in the country.
But the missiles sent a message to more than just the extremists in Iraq and Syria, General Ramazan Sharif of the Guard told state television in a telephone interview.
"The Saudis and Americans are especially receivers of this message," he said.
"Obviously and clearly, some reactionary countries of the region, especially Saudi Arabia, had announced that they are trying to bring insecurity into Iran."
Sunday's missile strike came amid recent confrontations in Syria between US-backed forces and pro-government factions.
The US recently deployed a truck-mounted missile system into Syria as Assad's forces cut off the advance of America-backed rebels along the Iraqi border.
Meanwhile, the US on Sunday shot down a Syrian aircraft for the first time, marking a new escalation of the conflict as Russia warned it would consider any US-led coalition planes in Syria west of the Euphrates River to be targets.
The Zolfaghar missile, unveiled in September 2016, was described at the time as carrying a cluster warhead and being able to strike as far as 700 kilometres (435 miles) away.
That puts the missile in range of the forward headquarters of the US military's Central Command in Qatar, American bases in the United Arab Emirates and the US navy's 5th Fleet in Bahrain.
The missile could also strike Riyadh, the capital of Saudi Arabia.
While Iran has other ballistic missiles it says can reach longer distances, Sunday's strike appears to be the furthest carried out abroad.
Iran's last foreign missile strike is believed to have been carried out in April 2001, targeting an exiled Iranian group in Iraq.
Iran has described the Tehran attackers as being "long affiliated with the Wahhabi", an ultraconservative form of Sunni Islam practised in Saudi Arabia.
However, it stopped short of directly blaming the kingdom for the attack, though many in the country have expressed suspicion that Iran's regional rival had a hand in the assault.
Since Mr Trump took office, his administration has put new economic sanctions on those allegedly involved with Iran's missile programme as the Senate has voted for applying new sanctions on Iran.
However, the test launches have not affected Iran's 2015 nuclear deal with world powers.
Israel is also concerned about Iran's missile launches and has deployed a multilayered missile defence system.
When Iran unveiled the Zolfaghar in 2016, it bore a banner printed with a 2013 quote by Khamenei saying that Iran will annihilate the Israeli cities of Tel Aviv and Haifa should Israel attack Iran.
Israeli security officials said on Monday they were studying the missile strike to see what they could learn about its accuracy and capabilities.
"We are following their actions. And we are also following their words," Israeli Prime Minister Benjamin Netanyahu said.
"And I have one message to Iran: Do not threaten Israel."
Iranian officials meanwhile offered a series of threats of more strikes, including former Guard chief General Mohsen Rezai.
He wrote on Twitter: "The bigger slap is yet to come."