A senior Palestinian official on Tuesday accused Israel of the "deliberate execution" of two Palestinian teenagers shot dead by border policemen in a clash in the West Bank last week.

But an Israeli army spokesman told AFP that video footage purporting to show the two being killed without provocation on Thursday had been doctored, a claim shared by the defence minister.

"In the strongest possible terms, we condemn the deliberate execution of two Palestinian teenagers who were fatally shot with live ammunition outside Ofer prison last week," the Palestine Liberation Organisation's Hanan Ashrawi said in a statement.

"Both boys were unarmed and posed no direct or immediate threat."

"Israel's use of excessive and indiscriminate violence and live ammunition at non-violent Palestinian demonstrations constitutes war crimes and crimes against humanity under international law," she said.

The military said at the time that the border police had used "anti-riot means and rubber bullets" against a violent demonstration by about 150 Palestinians.

Defence for Children International Palestine has released what it said was CCTV footage showing the deaths of Musaab Nuwarah, 20, and Mohammed Udeh, 17, during Thursday's demonstration near the prison.

The protest was to mark the 66th anniversary of the Nakba -- or "catastrophe" -- of the Jewish state's creation.

The video can be seen on the Swiss-based non-governmental organisation's website: http://www.dci-palestine.org/documents/israeli-forces-shoot-and-kill-two-palestinian-teens-near-ramallah.

It is interspersed with an account of events by a Palestinian man.

"That film was edited and does not reflect the reality of the day in question; the violence," Major Arye Shalicar, an Israeli army spokesman, told AFP.

The border police contingent was under the army's command at the time.

"As part of our enquiry we have investigated whether there was live fire and we have not found that there was live fire," he said. "We are continuing with our investigation."

Defence Minister Moshe Yaalon also spoke of doctored images and told journalists that Thursday's incident was "violent, during which stones and petrol bombs were thrown at police who, feeling threatened, acted as they should have."

But Israeli rights group B'Tselem rejected the army's version and said late Tuesday that two other Palestinians aged 15 and 23 were also hit by live fire outside Ofer prison and wounded.

- 'Killing was wilful' -

B'Tselem said it had obtained video footage from four security cameras in the area showing that four Palestinians were shot last week by Israeli troops.

It said it had "strong evidence that live ammunition was used (by the army) and that the fire hit the upper torsos of all four victims".

"The investigation, compounded by security camera footage of the incident, indicates that the circumstances of the incident in no way justified use of live fire. These findings raise grave suspicion that the killing was wilful."

Amnesty International has denounced the army's "excessive" use of force in the Ofer incident.

"The Israeli army and border police used excessive, including lethal, force in response to rock-throwing protesters who could not have posed a threat to the lives of the soldiers and policemen in or near the fortified military camp," the rights watchdog said last week.

A senior UN official called on Israel to carry out an "independent and transparent" investigation into the death of the teenagers.

Oscar Fernandez-Taranco, the assistant UN secretary general for political affairs, also urged Israel to ensure that troops "strictly respect" guidelines on the use of force and firearms.