UN Secretary General Ban Ki-moon was unharmed but appeared shaken Thursday after a rocket landed near the Baghdad office of the Iraqi prime minister.

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Bodyguards rush to protect Iraqi Prime Minister Nuri al-Maliki and UN Secretary General Ban Ki-moon as a mortar round lands in a garden 40 metres away from their press conference in Baghdad. ((Sabah Arar/Associated Press))

Ban ducked behind a podium whilehe and Nouri al-Maliki were holding a news conference.

Small chips of debris floated down from the ceiling above the UN chief after the explosion rattled the building in the Green Zone.

Al-Maliki's security officials said it was a rocket attack.

The explosion caused a crater one metre in diameter and about 50 metres from the building where the news conference was in progress, according to an AssociatedPress reporter.Two cars were damaged.

Al-Maliki said "nothing's wrong" as one of his security men started to grab the prime minister. Within minutes, the two men resumed their news conference.

Ban's meeting with al-Maliki isthe first visit by the top United Nations official in nearly 18 months, UN officials said.

Ban will be in the Iraqi capital for only one day of meetings with Nouri al-Maliki, whose forces are working with the U.S. military in a major operation to curb violence in Baghdad and the surrounding territory.

The UN officials, who spoke on condition of anonymity because they were not authorized to release the information, would give no other details about the visit.

The top UN official was last in Baghdad when Ban's predecessor, Kofi Annan, visited the capital in November 2005.

With files from the Associated Press