Government officials and police who have worked with the occupation authorities have become frequent targets in recent months. A State Department official remarked that yesterday's attack was at least the third at a Green Zone checkpoint since January.
After the attack, British Prime Minister Tony Blair spoke out forcefully to squelch speculation in London that his government was eager to find an "exit strategy." Britain has 7,500 troops in Iraq and provides the strongest support overseas for Bush administration policies.
"What has happened in Iraq today ... underlines this fact: We are not going to have any so-called quick exit, there will be no cutting and running in Iraq," Blair told a news conference on a visit to Turkey.
"You have got to transfer sovereignty to the Iraqi people. It's clearly time for the occupation to end," Condoleezza Rice, President Bush's national security adviser, said yesterday in Berlin.
"It's clearly time for Iraqis to be in control of their own political future."
U.N. envoy's role
Amid the constant security threats, United Nations envoy Lakhdar Brahimi is trying to assemble an interim "caretaker" government that will hold power until elections for a national assembly early next year.
By the end of this month, Brahimi hopes to pick a president, two vice presidents, a prime minister and a Cabinet controlling 30 ministries.
But his plan to appoint officials who don't hold political ambitions has drawn the ire of current Governing Council members, who want to hold on to their power and influence.
With the shape of the new power structure still largely unknown, "there is a real possibility that the new government will not be seen as having enough legitimacy," said Crocker of CSIS.
Questions also surround the future control of Iraqi oil revenues, a continuing investigation into corruption during the United Nations' oil-for-food program, Iraqi development funds, and the Iraqi security forces now being trained and equipped by the United States.
U.S. administrator L. Paul Bremer III, meanwhile, has granted broad powers to a series of commissions with five-year terms that appear to undercut the authority of future ministers.
Yesterday's assassination shows how dependent any new Iraqi government will be on the continued presence of American forces to provide security.
But Michael Eisenstadt, a military specialist at the Washington Institute for Near East Policy, said:
"The longer we stay, the more antipathy our presence creates and the less freedom of action we have to do what we have to do to justify our presence."