Cairo, Egypt ? Osama bin Laden endorsed the new leader of al-Qaida in Iraq in an Internet posting Saturday, and he warned Shiites there against collaborating with the United States in its fight against Sunni insurgents.

In his fifth audio message this year and his second in two days, bin Laden also warned nations not to send troops to Somalia, where Islamic militants have taken control of the capital and much of the south.

Saturday’s message came as Iraqi Prime Minister Nouri al-Maliki, a Shiite, started a regional tour seeking support from Sunni Arab countries for his national reconciliation plan that contains a conditional amnesty for insurgents excluding al-Qaida members.

Notably, bin Laden’s voice in the 19-minute recording was much stronger than in the message that appeared Friday on the Web, reflecting the defiance of its content.

The authenticity of the recording could not be immediately verified. It was accompanied by a photo of bin Laden above the logo and name As-Sahab, al-Qaida’s media production wing.

This image released by IntelCenter on Saturday shows a photo of Osama bin Laden above the logo and name As-Sahab, al-Qaida's media production wing, as it appears on an Internet message Saturday with a 19-minute audio recording.

In Washington, the Bush administration said it was reviewing the tape and trying to determine its authenticity.

Although no date was given for bin Laden’s message, it was probably made after June 12, when al-Qaida announced that Abu Hamza al-Muhajer was the new head of its operations in Iraq.

Bin Laden gave his support to al-Muhajer, the replacement for Abu Musab al-Zarqawi, who was killed in a U.S. airstrike June 7.

Bin Laden’s message Saturday also urged the leaders of al-Qaida in Iraq to work with other militant groups operating there.