Leading article: Mercenaries and murder

Has ever a claim of progress been so comprehensively undermined? Last week, the US commander in Iraq, General David Petraeus, gave a startlingly optimistic analysis of the security situation in the country to Congress, a message he repeated yesterday on a visit to London. Yet within days of this first testimony, a key tribal ally of the US, Abdul Sattar Abu Risha, was murdered in a bombing outside his home. And now we learn of a terrible incident on Sunday, in which a private US security company, Blackwater, killed 11 civilians after firing into a crowd in the Mansour district of Baghdad.

The roots of this latest atrocity lie in the aftermath of the initial invasion. After Saddam Hussein's regime was toppled in 2003, private security companies employing ex-servicemen flooded into the country. Blackwater was one of the biggest. It had been employed by the US State Department to guard its officials and diplomats. The rewards have been huge. Blackwater is reported to have a contract worth $300m.

Yet the legal status of these companies is hazy. Their personnel are neither civilian nor military, and they are also, apparently, immune from prosecution. The proliferation of such companies raises some uncomfortable questions about the use of private forces to perform military duties. In another age, former soldiers selling their services would have been described as mercenaries. There is an unpleasant smell of political corruption about their growth, too. Many of these security companies have links with the White House and Congress, the institutions that are funding them.

But most damning of all is what their presence says about the state of Iraq. The US Ambassador to Iraq, Ryan Crocker, spoke of the importance of the role of private contractors before Congress last week. But the fact that these contractors are needed at all shows that Iraq remains deeply unstable. They are doing a job that ought to be the province of the Iraqi army or police. That US diplomats have to rely on what is, in effect, a private army for security, four years after toppling Saddam, shows what a fiction recent claims of Iraq's "progress" are. And bloody episodes like Sunday's are one of the reasons the US presence in Iraq continues to be so resented by the local population.

Now the Iraqi government has revoked Blackwater's licence to work in Iraq and will review the status of all private security firms operating in the country. The US Secretary of State, Condoleezza Rice, was busy trying to mend bridges with Baghdad yesterday. But this affair is not merely a condemnation of the use of private contractors. It is a damning indictment of the way the White House has pursued its objectives in Iraq from the start.