In a videotape broadcast Thursday by the Qatari-based al-Jazeera television, Zawahiri said al-Qaida cannot stay idle "watching our brothers in Gaza and Lebanon being killed" but will make "all countries participating in the crime against our brethren pay the price."
Zawahiri, whose comments implied that al-Qaida is threatening to intervene in the raging confrontations between Israel and Hezbollah and Hamas, said "Muslims in Gaza and Lebanon are being subjected to a Zionist-Crusader war."
Zawahiri urged all the "oppressed Muslims" to get together and make an alliance to fight against Israel and its supporters.
"As they band together to fight us, we should assemble to fight them too," he said.
"The bombs and shells tearing apart the bodies of our people in Lebanon and Palestine are not strictly from Israel but they are being supplies and financed by all the Crusader countries and therefore everyone who takes part in this crime should pay," Zawahiri added.
He also vowed to shift the "jihad" (holy Muslim war) later from Iraq to the borders of Palestine.
Israel has been locked in military operations against Hamas in Gaza and Hezbollah in the north following the kidnapping of its soldiers by the two Islamic militant groups.