By Louis Charbonneau

UNITED NATIONS, April 3 (Reuters) - U.N. Secretary-General Ban Ki-moon dismissed as "totally false" accusations made by al Qaeda's deputy chief that the United Nations was not helping Muslims, a U.N. spokeswoman said on Thursday.

In a new audio message released on Wednesday, al Qaeda deputy leader Ayman al-Zawahri denounced the United Nations, vowed to attack Jews both within and outside Israel and said al Qaeda leader Osama bin Laden was alive and well.

Ban discussed the message with Afghan President Hamid Karzai at a breakfast meeting in Bucharest on the sidelines of a NATO summit, U.N. spokeswoman Marie Okabe told reporters.

"Both (Ban and Karzai) noted, contrary to that message, the contributions that the United Nations has made to the Muslim world," she said.

Ban also met with U.N. employees in Romania on Thursday, Okabe said. They, too, asked about the Zawahri recording.

"He described as a totally false and unacceptable accusation that the United Nations did not help the Muslim world," she said.

In the message, Zawahri defended attacks on U.N. offices in an apparent reference to twin bomb attacks on U.N. buildings in Algiers, which killed 41 people in December 2007, and the 2003 bombing of a U.N. building in Baghdad that killed 22.

"The United Nations is an enemy of Islam and Muslims," he said. "It has legalized the creation of the state of Israel and its seizure of Muslims' land ... it has legalized the crusader presence in Afghanistan ... and Iraq," he said in a 104-minute audio recording posted on the Internet.

Okabe declined to say whether the United Nations had increased security as a result of the message. "As you know, the security (department) at the U.N. is constantly reviewing security around the globe 24 hours a day, and we would not get publicly into what those measures are," she said.

(Editing by Patricia Zengerle)