Al-Qaeda ideologue Ayman al-Zawahiri has urged Palestinians to reject a referendum on a future state.
Zawahiri has appeared several times on videos
Palestinian Authority President Mahmoud Abbas wants Palestinians to be able to accept or reject a two-state solution.
But the vote is opposed by the Hamas party, which won elections in January and is committed to destroying Israel.
Zawahiri, in a video on al-Jazeera TV, also praised militant leader Abu Musab al-Zarqawi. The channel said the video was made before Zarqawi's death.
"God bless the prophet of Islam in Iraq, the persistent hero of Islam, the Holy Warrior Abu Musab al-Zarqawi," Zawahiri said.
He also encouraged Iraqi insurgents, "who are confronting crusaders and their apostate aids and the merchants of religion".
In his comments on the Palestinian referendum - which could take place as early as next month - Zawahiri said: "Palestine is not for bargaining or bidding."
He repeatedly wagged his right finger as he made his declaration, dressed in a white turban and tunic, with an automatic weapon at his side.
Zawahiri went on: "Palestine was a land of Islam, and its liberation is the duty of every Muslim."
He called on Muslims everywhere to support the Palestinian people.
The video also made references to political tensions in his homeland, Egypt, and to Sudan's strife-torn region of Darfur.
It accused UN officials visiting Sudan of preparing "to occupy and divide it".
"I call upon every Muslim and everyone who has faith in Sudan, and every fervent Muslim in Darfur to confront the Zionist Crusader plot to occupy the lands of Islam," Zawahiri said.
The al-Qaeda deputy leader was last seen in a video in April, saying Iraqi insurgents had trounced US forces.
Al-Jazeera did not say how it obtained the latest 17-minute tape.