Which militia groups does Iran support in Syria - and across the Middle East?
Iran's so-called "axis of resistance" is a key part of its foreign policy, which it uses to wield influence across the Middle East while reducing that of its rivals - the US and Israel on the Western side - and Saudi Arabia.
Friday 27 October 2023 15:52, UK
Iran has been at the centre of discussions around the Israel-Hamas war.
Although it has denied any direct involvement in the incursion of 7 October, Iran's supreme leader Ayatollah Ali Khamenei said it "kisses the hands of those who planned the attack on the Zionist regime".
Fears of it directly entering the conflict with Israel have spiked after the US launched retaliatory strikes on two Iranian-linked sites in Syria following attacks on American facilities there.
Iran's Revolutionary Guard and its elite Quds Force gives out millions of dollars in funding to arm and train militia groups throughout the Middle East to assert power in the region.
This so-called 'axis of resistance' is a key part of Iran's foreign policy, which it uses to wield influence while reducing that of its rivals - the US and Israel on the Western side - and Saudi Arabia.
Here Sky News looks at the different forces in countries throughout the Middle East that are backed by Tehran.
Syria
Iran's military, security and intelligence services have long assisted its Shia allies in Syria to help prop up Bashar Al Assad's government there.
Strategically, as well as Assad's army, it has also backed several pro-government militia groups in case his regime falls.
The year after the Syrian civil war began, a pro-government militia formed called the National Defence Forces (NDF).
It was by far the largest in the country, with around 40,000 fighters, who were from the Alawite, Druze and Sunni communities.
Iran called for Assad to legitimise the NDF and formally absorb it into the army, but in 2016 the regime decided to dismantle it, forcing the Islamic Republic to focus on the Local Defence Forces (LDF) instead.
Unlike its predecessor, the LDF became part of the Syrian army, with around 50,000 fighters - recruited mostly from Aleppo and Raqqa.
Within the umbrella organisations, elite forces such as the Al Sefira Corps, Al Bagir Brigade and the Qatraji forces were considered the most powerful.
Smaller groups of Shia militias also operate in Syria, including ones Iran has helped recruit from Afghanistan and Pakistan.
Palestinian territories
Iran provides funding and weapons to both Hamas and its smaller rival Islamic Jihad in the Palestinian territories.
Palestinian Islamic Jihad gets more funding per head than Hamas, according to military analyst Professor Michael Clarke.
But along with other hardline Palestinian groups, such as the Popular Front for the Liberation of Palestine (PFLP) and the Democratic Front for the Liberation of Palestine (DFLP), they're "small and not very well organised".
"It's not so much the size of the forces that Iran is interested in," he says.
"It's more that they like to spread their largesse, as you never know who will emerge on top. So it's a good investment to make sure you're helping all of them."
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Analysts believe Hamas's use of drones to help overwhelm Israel's famous Iron Dome defence system in the 7 October attack is proof of Iranian involvement.
Despite their shared anti-Israel agenda, Hamas and Iran have disagreed over various issues in recent years.
Tehran temporarily withdrew funding from Hamas when it came out in support of anti-Assad protesters in Syria during the civil war.
Lebanon
Iran spends more money and resources on Hezbollah than any other group in the Middle East.
Its heavy presence in southern Lebanon, near the border with Israel, makes it of huge strategic importance to Tehran.
"Hezbollah are Iran's main client in that part of the world - and their biggest investment," Professor Clarke says.
"They give them some of the best weapons, including Fateh 1-10 ballistic missiles and armoured vehicles.
"So while the others just look like terror groups, Hezbollah is more like a conventional military force."
Iran also used Hezbollah to train pro-Assad forces in Syria during the civil war.
"They use them as a conduit to other groups," Professor Clarke adds. "Even though Hezbollah doesn't have a great interest in anything beyond Lebanon and southern Israel, they have to do what they're told by Tehran."
Fire over the Israeli-Lebanese border since war broke out on 7 October has sparked fears Hezbollah could directly enter the conflict - leading to a wider-scale war between Israel, its Western allies and Iran.
Iraq
Before it disbanded in 2008, Iran backed the Mahdi Army - the leading Shia militia to take on US forces in Iraq.
Now it supports many of the 60-plus militias under the state-sponsored umbrella organisation the Popular Mobilisation Forces (PMF).
The PMF officially formed in 2014 to help fight Islamic State.
Yemen
Iran uses the Houthi rebels, one of three groups fighting for power in Yemen, as a "proxy force" to put pressure on its two main rivals in the region, Israel and Saudi Arabia.
Professor Clarke says: "The Houthis are prepared to make war on just about anybody.
"They've attacked both Saudi Arabia and Israel with Iranian missiles, so it suits the Iranians to keep the Houthis going because they're such a disruptive force for everybody."
The first US military intervention in defence of Israel since war broke out at the beginning of the month was to shoot down three missiles launched by Houthis from Yemen.