Baghdad, Iraq ? The U.S. military decided Tuesday to conduct an accelerated inquiry to learn why American troops opened fire, killing an Italian intelligence agent and wounding an Italian journalist he helped rescue from insurgents in Iraq.

The decision to fast-track the investigation into the attack, which has strained relations with Italy, a key American ally, came as the military also opened an inquiry into the shooting death of a Bulgarian soldier. That death appeared to be another friendly fire incident on the same day.

Both probes were an indication of the pressure being brought on the Bush administration by the few American allies in Europe that have steadfastly supported his policies in Iraq.

Italy and its prime minister, Silvio Berlusconi, sent 3,000 troops to Iraq, while Bulgaria has 460. Both countries have said they will not withdraw their troops, but domestic pressure to bring them home has been growing — especially in Bulgaria where it has become an election issue.

The shooting Friday that killed intelligence officer Nicola Calipari and wounded Giuliana Sgrena, a 56-year-old journalist for the left-wing Il Manifesto newspaper, angered Italians and rekindled questions about the country’s involvement in Iraq.

In Bulgaria, the death of Pvt. Gardi Gardev made the country’s presence in Iraq an issue ahead of elections in June. Opinion polls showed a growing majority of Bulgarians oppose the deployment. The opposition party has promised a withdrawal if it wins the election.

In Rome, Berlusconi’s office said the premier had “expressed the satisfaction of the Italian government” at the accelerated U.S. military investigation.

President Bush called Berlusconi on Friday and promised a full investigation into the shooting, which took place after nightfall as the car carrying Sgrena, Calipari and two other agents approached Baghdad airport. Another agent also was wounded.

Italian Foreign Minister Gianfranco Fini told parliament Tuesday that U.S. troops killed Calipari by accident, but disputed Washington’s version of events.