From ballistic missiles to unmanned drones, Yemen's Huthi rebels appear to have bolstered their fighting capabilities, posing a serious threat to mighty neighbour Saudi Arabia.
In June alone, the Iran-aligned Shiite Huthis launched at least 20 missile and drone attacks on the oil-rich kingdom, Iran's regional foe, some resulting in casualties and damage.
Saudi advanced air defences successfully intercepted most of the strikes but failed to deal with some, including a drone attack on the vital airport of Abha, in the south, that killed one person and injured 21 others.
"We have witnessed a massive increase in capability on the side of the Huthis in recent years, particularly relating to ballistic missiles and drone technology," Andreas Kreig, a professor at King's College London, told AFP.
"The current capability is far more advanced than anything the Yemeni armed forces had before the civil war," which began in 2014, said Kreig, an expert on the Middle East.
The rebels showed off some of their advanced weaponry at an exhibition held earlier this month at an undisclosed location to mark the fifth anniversary of their offensive against the Yemeni government.
Footage distributed by the Huthis showed models of at least 15 unmanned drones and various sizes of missiles of different ranges.
The newest of these weapons were long-range cruise missiles, dubbed "Al-Quds", and explosives-laden "Sammad 3" drones that can hit targets as far as 1,500 kilometres (932 miles) away, according to the Huthis.
- "Made in Yemen" -
On the sides of the Sammad 3, the phrase "Unmanned Aircraft Force" is printed, while the cruise missile is marked "Made in Yemen" on its giant body.
AFP has not established from independent sources if these missiles and drones were manufactured in Yemen.
Since 2014, the Huthis have controlled the capital Sanaa and vast swathes of north, central and western Yemen.
Forces of the internationally-recognised government with the backing of a Saudi-led coalition have been trying to retake these territories.
The conflict has killed or wounded tens of thousands of people and resulted in the world's worst humanitarian crisis, according to the United Nations.
Up until the end of 2018, the Huthis frequently used ballistic missiles they captured from Yemeni army depots to attack targets inside Saudi Arabia.
However, since the start of this year, they have shifted to Qasef 2 drones, a small booby-trapped aircraft that can evade radar detection but whose range is unknown.
The most serious attack took place on May 14 when Huthis used seven drones to target two pumping stations on Saudi Arabia's key east-west pipeline, shutting it down for several days.
"This is the first time the Huthis have demonstrated an apparent capability to hit a target 800 kilometres in Saudi territory with UAVs (drones)," Jane's 360, a defence and security think-tank, said in May.
"The attack on the pumping stations highlights the persisting risk of Huthis targeting of hydrocarbon infrastructure in Jeddah, Yanbu, and potentially cities such as Riyadh," said Jane's 360.
It said Saudi ports, military installations and airports were also at risk of further attacks.
OPEC kingpin Saudi Arabia spent some $65 billion on arms purchases last year, becoming one of the five biggest defence spenders alongside the United States, China, India and France, according to the Stockholm International Peace Research Institute.
- "Miracle" -
A Yemeni army retired brigadier, Jamil al-Mamari, believes the "Huthis are not capable of manufacturing missiles in Yemen... They are only capable of assembling and modification".
"Huthis keep modifying army missiles by boosting their explosive capability and adding remote control devices," Mamari said.
Experts rule out the possibility that Huthis may have modified these arms on their own.
The rebels have also launched attacks with explosive-laden boats and tanks, heavy artillery and anti-tank missiles.
Hussein Ibish, a senior resident scholar at the Arab Gulf States Institute in Washington, believes Iran has had a hand in developing the Huthis' armaments.
The Huthis "have grown dependent on Iranian and Hezbollah support to maintain their current war posture", Ibish told AFP.
"Their current war posture and their missile technology and capability are mainly the result of direct support from Iran and Hezbollah. So it's very difficult to untangle this knot," he said.
The United States and Saudi Arabia have repeatedly accused Iran of supplying sophisticated weapons to the Huthis, a charge Tehran denies.
Tehran has also denied allegations by Riyadh that it had encouraged the Huthis to attack the kingdom.
The Huthis have repeatedly stressed their capability to manufacture arms and their leader Abdulmalek al-Huthi has said the development was "a miracle and a great result of steadfastness".