"I reaffirm to our brothers the fighters in Gaza and everywhere that the mujahideen against crusaders in various battle zones are willing to give their brothers in Gaza and everywhere training and preparation," al-Zawahri said.
Al-Qaeda often uses the term "crusaders" to refer to the West.
'World is our battlefield'
"The mujahideen in Gaza should not be upset if the space [of action] had been narrowed as the whole world is our battlefield against targets [representing] the crusader-Zionist campaign."
"The mujahideen in Gaza should not be upset if the space [of action] had been narrowed as the whole world is our battlefield"
Al-Qaeda has begun to place greater emphasis on the Israeli-Palestinian conflict - an issue many Arabs and Muslims are intensely mindful of - in an apparent effort to widen its support and influence there.
But intelligence officials see little evidence al-Qaeda has established a presence in Palestinian areas.
Al-Qaeda has in the past criticised Hamas for dropping suicide bombings to play a political role.
Without naming Hamas, al-Zawahri advised the group against joining with non-Islamist factions under the umbrella of the Palestine Liberation Organisation (PLO), which is led by Mahmoud Abbas, the Palestinian president.
Abbas's Fatah movement is the largest of 11 groups that constitute the PLO, which in the early 1990s signed peace accords with Israel that aim to establish a Palestinian state.
"Talk of fixing the Palestine Liberation Organisation is futile," said Zawahri.
"The PLO is a secular entity that does not uphold Islamic law and it is the entity that dropped jihad from its covenant."
In his recording, titled "From Kabul to Mogadishu", al-Zawahri also called for Afghans to rally around Taliban fighters, for Yemeni tribes to fight US influence and for Somalis to reject any possibility of a "secular constitution".
Earlier in the month, Sheikh Sharif Ahmed, Somalia's new president, selected the Western-educated son of a murdered former leader to be prime minister in a power-sharing government intended to end civil conflict in the country.