An Israeli human rights group said yesterday it was investigating claims that an apparent surgical strike on a Hamas missile truck in Gaza, which is being publicised by Israel's armed forces on its website, is a case of mistaken targeting that has left eight civilians dead.

Monochrome images of the attack have been repeatedly shown by media around the world after being released by the Israeli Defence Forces (IDF) to demonstrate both the accuracy of their attacks and that Hamas was trying to move and hide rockets. The footage was also posted on the Israeli military's YouTube site.

However, the Israeli-Palestinian B'Tselem group in Gaza has testimony from the owner of the truck, as well as photographs taken at the scene, which appear to suggest that the vehicle was being used to transport gas welding canisters from a metalworking shop.

The air attack took place at 6pm on Monday in Salah al-Din street in Jabaliya. The grainy thermal imaging footage taken by the Israeli Predator drone that launched the rocket against the truck showed ghostly figures clustered around a vehicle loaded with what the Israeli airforce described as missiles being moved to a safe hiding place by Hamas fighters.

According to testimony supplied by truck owner Abu Imad-Sanur, members of his family had been trying to salvage material from a metal workshop he owns next door to a bombed house. The canisters, he claimed, were being moved to prevent looting.

He named the dead as Muhammad Bassel Madi, 17, Wisam Akram Eid, 14, Imad Ahmad Sanur, 32, Rami Sa'adi Ghabayan, 24, Mahmoud Nabil Ghabayan, 14, Ashraf al-Dabagh, 26, Muhammad Majed Ka'abar, 20, and Ahmad Ibrahim Khila, 15. Imad-Sanur denies any connections with militant organisations in the Gaza Strip that have been blamed for targeting Israeli towns with rockets.

The pictures released by B'Tselem yesterday - which it says were taken at the site - show the burnt-out wreckage of a truck that appears to have been loaded with scrap metal and gas welding tanks, with the gas valves still attached. An undamaged tank, apparently thrown out of the vehicle by the explosion, is identical in shape to the burned ones.

"I own a metalworks near the Palestinian Red Cross,' said Imad-Sanur in his testimony. "On Monday I was told a metalworking shop had been blown up, so I collected my sons to go there. When we arrived we saw that the house next door [understood to belong to a Hamas official] had been completely destroyed. There was a 10-metre-deep crater. Some of the walls had caved in into my shop.

"I was afraid people would steal my stuff and decided to move it."

It was while his son Imad was directing the loading of the second truckload that it was hit while Imad-Sanur - who suffers from asthma - was standing across the road to avoid the dust. "Friends and neighbours had come to help. Imad was standing on the truck. Suddenly I saw a huge flash and heard a booming sound. I started running and saw bodies everywhere. One of them was Imad. That was when I fainted."

Imad-Sanur told the Guardian yesterday: "I'm not satisfied with what's going on. Please, we want peace. Who wants his children to die? Who hates peace? The Israeli account is absolutely wrong. The pickup is still there and the oxygen cylinder is still next to it. Anyone can come and look at it."

Sarit Michaeli, a spokeswoman for B'Tselem, said that while her organisation had not been able to verify Imad-Sanur's claims that he was not involved with militants in Gaza, his story that he was moving welding equipment seemed believable. "What this emphasises is that this incident needs to be investigated by the IDF, lessons learned and if necessary people retrained. It is impossible to avoid civilian casualties, but in this case it is clear that an investigation is required."