By Rob Watson BBC News defence and security correspondent

Counter-terrorism officials have been digesting the first video appearance said to be by Abu Musab al-Zarqawi, the leader of al-Qaeda in Iraq.

The video is said to be the first showing Zarqawi

In the video, he called on Islamic militants to join together to drive the Americans out of Iraq.

He also dismissed the formation of any new government in Iraq as a puppet of the US.

There is broad agreement among counter-terrorism officials that this first ever video appearance is highly significant.

But there is less agreement on exactly what it means. Some analysts see it as a clear sign of weakness.

They say al-Zarqawi effectively admitted that he had been demoted in the insurgency with the formation in January of a coalition of Sunni extremist groups known as the Mujaheddin Shura Council - of which he is a member, not the leader.

By God, your dreams will be defeated by our blood and by our bodies - what is coming is even worse Abu Musab al-Zarqawi Zarqawi message: excerpts

Some say the video also shows he is clearly very worried about the formation of a new government in Iraq and the increasing efforts by the US to reach out to Sunni tribal and other leaders.

But other counter-terrorism officials are not so sure. They believe the video could be seen as al-Zarqawi reasserting his leadership.

The US continues to describe al-Zarqawi as a real threat and blame him for 90% of the suicide attacks in Iraq.

That said, al-Zarqawi's role and that of other foreign fighters in the insurgency should not be overstated.

US officials believe the real backbone of the insurgency continues to be disaffected Iraqi Sunnis - many of them former members of the Iraqi military and intelligence services.