UN chief Ban Ki-moon has been left shaken by a blast which interrupted a news conference with Iraqi Prime Minister Nouri Maliki in Baghdad.
As Mr Ban was speaking during the live televised event, a mortar round or rocket landed about 100 metres (330ft) from the building, causing him to duck.
Mr Ban appeared frightened but neither he nor Mr Maliki was hurt.
The UN chief had earlier arrived on his first visit to Baghdad since he took office in January this year.
The BBC's Hugh Sykes in Baghdad says buildings and windows shook when the huge bang reverberated throughout the city shortly after 1530 (1230 GMT).
He says it appeared to be caused by a mortar or rocket attack on the international zone, otherwise known as the Green Zone, where all the diplomats and most of the US military are, in the centre of Baghdad.
Iraqi television showed Mr Ban and Mr Maliki seated at a desk, as a reporter asked a question.
Suddenly there was a bang, at which moment the camera shook and juddered to the left.
Mr Ban flinched and momentarily half-ducked behind the table before recovering his composure. Mr Maliki did not react.
Small pieces of debris could be seen floating down from the ceiling above Mr Ban.
Both men continued answering questions following the attack.
A UN spokesperson said the mortar or rocket had landed in an open field.
Earlier, Mr Ban and Mr Maliki held an hour-long talk following Mr Ban's arrival, which had been kept secret.
His visit is the first to Iraq by a UN chief since Mr Ban's predecessor Kofi Annan went to Baghdad in November 2005.
Mr Annan pulled all UN staff out of the country after the former UN ambassador to Iraq, Sergio Vieira de Mello, and 21 other people died in a huge explosion at the UN headquarters in Baghdad in August 2003.
In a fresh attempt to control the violence, Iraq's government says it has begun holding direct talks with some militant groups.
On Thursday morning, Mr Maliki met Ahmed Shibani, a senior aide to radical Shia cleric Moqtada Sadr, whose political movement plays a key role in Iraq's power-sharing coalition.
Mr Shibani was freed from US custody a day earlier, after being held for more than two years.