The men were working with a Kuwaiti subsidiary of Saudi company Al-Tamimi which had been subcontracted to supply foodstuffs to US occupation forces in Iraq.
The tape displayed the decapitated bodies of the two Pakistanis, but Aljazeera declined to air it citing viewer sensitivities.
The same group said it had freed an Iraqi driver after he had proved that he was deluded and had announced his repentance.
Last week, the Pakistani foreign ministry said that two nationals, Raja Azad Khan and Sajjad Naeem, were identified as missing.
Although Aljazeera would not air graphic footage it did replay scenes showing the Pakistani captives giving their names and identity papers verifying their positions as contractors to Kellogg, Brown and Root, the construction arm of US-based company Halliburton.
The captors also displayed a picture of the two Pakistani men hugging a US military officer in Iraq.