Crude barrel bombs killed scores of people in the Syrian city of Aleppo this week, in a string of devastating attacks that suggest the Syrian military is turning to increasingly deadly homemade weapons, experts say.

Unverified videos of the attacks uploaded to YouTube show residents hurrying down rubble-strewn streets, through thick clouds of dust to evacuate damaged buildings and help those injured in the blasts.

More than 100 people died in the first bombing on Sunday, according to Human Rights Watch, making it one of the deadliest days of the war since chemical weapons killed hundreds of people in a Damascus suburb on Aug. 21.

The Aleppo attacks continued until Wednesday, killing at least another 36 people, Human Rights Watch said. According to its investigation, in each case it appears that Syrian military transport helicopters dropped homemade bombs likely made of metal barrels stuffed with explosives, oil, and shrapnel on neighbourhoods controlled by opposition fighters.

hi Aleppo Syria barrel bomb damage

People run amid debris at a site hit by what activists said was an airstrike from forces loyal to Syria's President Bashar al-Assad, in the Tareek Al-Bab area of Aleppo, on Dec. 18. (Saad AboBrahim/Reuters)

Barrel bombs have been used by Assad’s forces for more than a year, but they‘ve become much more powerful and sophisticated over that time, according to Eliot Higgins, an influential British blogger who uses social media to glean information about weapons used in the conflict.

“They were pretty much simple pipe bombs, the early ones, and the problem they had is that they would fall through the sky and the fuse would burn out too soon and they would explode in midair — they weren’t terribly effective,” he said in a phone interview. “These new types are four to five times bigger than the original ones. They’re absolutely massive.”

DIY weapons on YouTube

Nearly three years into the conflict, with well over 100,000 people dead, there are few signs the fighting in Syria will soon come to an end. But far-flung observers such as Higgins have been able to track how do-it-yourself arms have evolved by scouring videos and other media depicting the war that are being posted online.

Opposition fighters have become known for using improvised weapons, setting up their own munitions factories, building their own grenades, mortar rounds, missiles, slingshots, catapults and rocket launchers, among other things. But Assad’s forces are turning to do-it-yourself weapons too, as they try to gain an upper hand in the vicious but slow-moving conflict.

“Everybody’s making weapons now in Syria,” said Joshua Landis, a Syria expert at the University of Oklahoma. “In many ways it’s an expression of the brutality of this war.”

Western countries have been reluctant to supply weapons to Syria's fractious opposition, leaving its fighters to do battle with any lethal contraptions they can muster. For Syria’s well-armed military, however, the motives for using modified and homemade armaments are less clear.

Ole Solvang, a researcher with Human Rights Watch who has visited the war-torn country, said the use of barrel bombs in Aleppo may be an inexpensive way for the Assad regime to preserve its stock of conventional aerial weapons.

“Over the last year or so the Syrian air force has been conducting attacks daily all over Syria,” Solvang said by phone from Paris. “It’s difficult to say how many bombs they have. They must start getting concerned at some point they would be running out.”

Barrel bombs are inaccurate weapons, making them particularly dangerous to civilians. In the case of the Aleppo bombings, Solvang said his organization has been struggling to determine whether the raids were aimed at opposition military targets, or whether Assad forces were indiscriminately bombing neighbourhoods controlled by opposition forces to terrorize residents.

"So far, I have to say it looks like there government is just dropping bombs all over the place,” he said.

Adapting to civil war

Higgins, who blogs under the pseudonym "Brown Moses," believes that regime forces are turning to homemade weapons as they try to adapt to civil war instead of their intended purpose, which was to repel a foreign invasion.

In the case of barrel bombs, he said the Syrian air force is likely trying to find a way to use its fleet of cargo helicopters as fighting machines rather than simply as transport aircraft.

'Everybody’s making weapons now in Syria.'— Joshua Landis, Syria expert at the University of Oklahoma

Higgins has also found evidence that the Syrian military is modifying weapons to make them more effective. One example, he said, is a small artillery rocket known as a “volcano” that has had its warhead removed and replaced with a much more powerful one. The result is a projectile with a short range that can “take down an entire building.”

A similar type of modified rocket, also referred to as a volcano by pro-regime fighters, was used in the Damascus chemical weapons attack in August, he said. That attack killed at least 300 people and injured more than 3,000 others, prompting U.S. President Barack Obama to threaten the Assad regime with airstrikes if it did not agree to destroy its chemical weapons stockpile.

The interesting thing about volcanoes, Higgins said, is that they’ve been linked to militia groups in Iraq that were backed by Iran, a close ally to Assad. Iran also supports the Lebanese militant group Hezbollah, which has been drawn into the Syrian conflict, fighting alongside Assad's forces.

“You start seeing links between Iran and Hezbollah to these munitions,” Higgins said. “Who helped [pro-regime forces] develop these weapons? Because they were developed during the conflict and not before it.”