The Israeli human rights group B'Tselem has concluded that footage capturing the moment two Palestinian teenagers were shot dead by Israeli soldiers despite posing no risk to them is "genuine and consistent", contradicting Israeli army claims that the footage is likely to have been forged.

A short section of edited CCTV footage was released earlier this week showing Nadim Nawara, 17, and Mohammad Salameh, 16, being shot and killed. Since then Israeli military sources have been quoted anonymously on several occasions in the local media trying to undermine the tape's credibility.

The two boys were killed on Thursday last week during a rally involving stone-throwing outside Ofer prison on the West Bank on "Nakba Day", when Palestinians mark the mass displacement that occurred during the establishment of the Israeli state in 1948.

When footage from CCTV cameras installed on a business close to the shootings was first circulated on Monday evening by the group Defence for Children International – Palestine, senior Israeli army sources suggested it had been edited in a "biased" and "tendentious" way.

By Thursday morning army sources were being quoted in Haaretz claiming either that the tape was a forgery or that an unknown Palestinian gunmen had killed the two youths and badly injured another.

The emergence of the CCTV footage this week, showing the moment of the pair's deaths, sparked international controversy as it sharply contradicted the initial Israeli police and military accounts of the day, which insisted no live ammunition had been used and the boys had died in the midst of violent clashes that had threatened the lives of soldiers.

Senior US and UN officials are among those who have called for a full inquiry, while the US secretary of state, John Kerry, has also raised his concern.

Several journalists from international news organisations were at the demonstration outside Ofer prison when the incident occurred, including CNN and a photographer for Agence France-Presse, Abbas Momani, whose still photographs appear to duplicate action from the CCTV images.

The full CCTV footage – amounting to hours of tape – was reviewed and logged by researchers for B'Tselem, which has provided copies to Israeli military police and planned to release more of the footage.

Invited by the Guardian to provide evidence the footage was faked, a senior Israeli military spokesman on Thursday would only say it had been edited to "misrepresent the extensive Palestinian violence that day", adding that the army's investigation was ongoing.

Sarit Michaeli of B'Tselem said on Thursday that researchers had now reviewed all the CCTV footage taken from the four cameras installed at the scene of the killings, showing several different angles. They concluded that the edited footage was consistent with the sequence of events as it was captured on the full-length tapes.

Michaeli said: "The footage is continuous, as you can see from the time stamps.

"It starts just before midday and finishes around three. Taken together it shows that there is a light demonstration with some stoning. Soldiers fire rubber bullets and teargas until the fatal shootings. Then you see the youths get shot and fall."

Footage shot by CNN of the killings appears to confirm this picture, showing Nadim Nawara throwing stones at one stage close to the building where he was shot and killed, but still at some distance from where witnesses have placed the closest Israeli soldiers.

Whether violence took place earlier or not, Israeli open fire regulations are unequivocal in stating that it is only permissible to use live rounds – or lethal force – against stone-throwers when there is an immediate risk to life.

Neither of the youths was throwing stones when they were killed, and one was walking away from the Israeli position, with his back to soldiers, when he was shot.

The wounds to the two boys and another boy who survived being shot appear consistent with small-calibre, high-velocity live rounds, including the described entry and exit wounds and the way the bullets travelled in the body.

Commenting on efforts to cast doubt on accounts of the affair in +972 online magazine, Dahlia Scheindlin, a public opinion analyst in Tel Aviv, attempted to explain recent comments: "Public figures are well aware that the postmodern mindset makes it hard to pin down facts.

"Throwing out theories, no matter how wild, raises doubts even if far-fetched. Using words inaccurately, or not admitting to one's actions is another form. Accusing the other side of full-out conspiracy and elaborate fabrications is another."