By Nick Childs BBC Pentagon correspondent

US intelligence says it is concerned the Iraqi leader, Saddam Hussein, could give chemical or biological weapons to a terrorist group as a way of pre-empting an American attack on Iraq.

Washington is also making a concerted effort to promote its case that Saddam Hussein cannot be trusted

Such a group may launch an attack itself as a way of distracting international attention away from Iraq, a US intelligence official told the BBC.

The official did not offer any evidence of this.

However, it is clearly one of the scenarios the US military is considering in its planning for a possible invasion.

US intelligence also says it has evidence of new efforts by Iraq in the last two months to protect or hide its suspected weapons of mass destruction, either from a possible attack or from new inspections.

The fate of Iraq's suspected arsenal is a major worry for US planners.

Washington has already voiced worries that Iraq could use chemical and biological weapons if the US launched an attack.

As the diplomatic stakes in this crisis are raised at the United Nations, Washington is also making a concerted effort to promote its case that Saddam Hussein cannot be trusted.