DUBAI, Feb 3 (Reuters) - Al Qaeda's deputy leader dismissed U.S. President Barack Obama's expression of concern over killings in Gaza as an empty gesture on Tuesday and said Washington remains a main enemy of Muslims.

"I remind our mujahideen brothers that our enemy in Gaza is not only Israel but the Zionist-crusader coalition, with America, the leader of evil ... at its head," Ayman al-Zawahri said in an audio recording posted on Islamic websites.

"Obama said he was concerned about the killings of civilians in Gaza. We thank Mr. Obama for his concern which we received with thousands of shells and ... white phosphorous," Zawahri said, referring to Israeli attacks on the Gaza Strip.

"But Obama's concern did not seem to last long as he did not say a word about Gaza in his inauguration speech, as if nothing had happened," he added.

"The Zionist-crusader (Israeli-Western) campaign against Is lam and the Muslims cannot be defeated without warfare," Zawahri said, calling the devout to join a jihad (holy war).

Then President-elect Obama broke his silence on Jan. 6 about the Gaza war and expressed deep concern about civilian deaths in Gaza and in Israel. He vowed to push for Middle East peace when he took power.

Israel waged a 22-day offensive against the Islamist Hamas group in Gaza earlier last month, killing some 1,300 Palestinians and injuring another 5,000.

The offensive, which Israel said was aimed at ending Hamas rocket attacks, left 13 Israelis dead, including three civilians killed by rockets.

Obama said last month that verbal attacks by al Qaeda and Zawahri on him showed they were "nervous".

"I think that when you look at the rhetoric that they've been using against me before I even took office ... what that tells me is that their ideas are bankrupt," Obama told Al Arabiya television, according to a transcript of the interview.

Obama has named former U.S. Senator George Mitchell as his envoy for the Middle East conflict and vowed to aggressively pursue peace.

(Reporting by Firouz Sedarat; editing by Michael Roddy)

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