United Nations Secretary-General Ban Ki-moon reacts to the noise from a loud explosion during a news conference with Iraq's Prime Minister Nuri al-Maliki in Baghdad in this March 22, 2007 image taken from video footage.

An Associated Press reporter who ran outside saw a 3-foot-wide crater about 50 yards from the building where the news conference was in progress in Baghdad's Green Zone, which also houses the U.S. Embassy. Two cars were damaged.

Security officials for Prime Minister Nouri al-Maliki said it was a rocket attack.

Small chips of debris floated down from the ceiling above the UN chief after the explosion rattled the building. Ban looked frightened, casting his eyes right and left as he rose after ducking below the podium where he was standing and answering questions.

Al-Maliki said "Nothing's wrong," as one of his security men started to grab the prime minister, and both men resumed their news conference within minutes. They ended the question and answer session shortly thereafter.

The sound of a weapon being fired - which sounded like a rocket launch - could be heard not far from the AP office, which is across the Tigris River east of the Green Zone.

The last time a UN secretary-general was in Baghdad was in November 2005, when Ban's predecessor, Kofi Annan, visited the capital.

A bomb exploded at UN headquarters in Baghdad in August 2003, killing 22 people, including the top UN envoy, Sergio Vieira de Mello.