TIMELINE: Messages attributed to al Qaeda's Zawahri

(Reuters) - Al Qaeda's second-in-command urged Muslims to continue attacks on "criminal" America and criticized U.S. president-elect Barack Obama for vowing to back Israel during his campaign.

At least 50 messages have been broadcast by Osama bin Laden, Zawahri and their allies since the September 11 attacks in 2001.

Following is a chronology of major statements attributed to Zawahri in the past year.

December 14 - Zawahri, in an audio recording, accuses Arab leaders of betraying the Palestinians by attending a Middle East peace conference in the United States and urges Muslims to keep fighting. Zawahri denounces Saudi Arabia and Egypt, saying they were serving Israel and U.S. interests.

December 16 - Zawahri says in a video posted on the Internet that Britain's handover of security in southern Iraq shows insurgents are gaining the upper hand there.

April 2, 2008 - In an audio message, Zawahri denounces the United Nations, vows to attack Jews both within and outside Israel and says bin Laden is alive and well.

April 18 - Zawahri mocks Bush's decision to suspend troop withdrawals from Iraq, saying the U.S. president was scared of admitting defeat. Zawahri also mocks hopes that the Awakening Councils, security units created by Sunni Arab tribal groups to fight al Qaeda in Iraq, will restore stability to the country.

April 22 - Zawahri says in the second and final installment of his answers to questions compiled by Islamist websites that The Islamic State in Iraq remains the main force confronting the "crusaders" and their collaborators.

-- Zawahri also says U.S.-led forces are losing the battle against the Taliban in Afghanistan.

June 4 - In an Internet recording, Zawahri urges Palestinians to step up suicide and rocket attacks against Israel.

August 11 - An audio tape purportedly made by Zawahri accused President Pervez Musharraf and other politicians of trying to destabilize Pakistan at the behest of the United States.

August 22 - Zawahri in a videotape on the Internet eulogizes militants killed in a suspected U.S. air strike in Pakistan's border region in July.

September 8 - Al Qaeda issues a video in which deputy group leader Ayman al-Zawahri accuses Iran of taking part in a Western "Crusader" war against Islam.

November 19 - Zawahri warns U.S. president-elect Obama in a new taped message that he will fail if he follows the policies of President George W. Bush. He also criticizes Obama for vowing to back Israel during his campaign.