A new audiotape attributed to Osama bin Laden is calling on Muslims to launch a jihad, or holy war, to stop Israel's offensive in the Gaza Strip.

The tape was posted Wednesday on Islamist Web sites where al-Qaida usually issues its messages.

The authenticity of the tape could not be immediately verified.

A White House spokesman, Gordon Johndroe, said the tape appears to show bin Laden's isolation and his efforts to stay relevant "at a time when al-Qaida's ideology, mission and agenda are being questioned and challenged throughout the world."

The spokesman said the tape also looks like a bid to raise money in what he called al-Qaida's ongoing propaganda campaign.

Some information for this report was provided by AFP, AP and Reuters.