Ban Ki-moon ducks for cover after the rocket attack in Baghdad on Thursday. (AP)

Baghdad, March 22 (Reuters): UN secretary-general Ban Ki-moon was left shaken but unhurt today on his first visit to Baghdad after a Katyusha rocket landed just metres from a building where he was giving a news conference.

Moments after telling journalists he might boost the UN presence in Iraq because of improved security, a thunderous blast sent shockwaves through the conference venue, startling Ban and sending him ducking for cover behind a podium.

Security guards grabbed hold of Iraqi Prime Minister Nuri al-Maliki who was standing next to Ban at the time and was dusted by small bits of debris that fell from the ceiling.

Without commenting on the explosion, which sent a large column of smoke into the air, Ban recovered his composure and took one further question before leaving the conference room.

Interior minister Jawad Bolani played down the incident afterwards “This was not a security breach. Things like this happen in Baghdad once or twice a week.”

A Reuters reporter at the scene said the rocket landed on a small building about 50 metres from the news conference venue, a guesthouse in the Prime Minister’s compound. The interior ministry said it landed in a field outside the compound.

Earlier, Ban praised Maliki’s “strong leadership” and said: “As we see the improved situation on the ground, I am considering to increase the presence of the UN.”

Tens of thousands of Iraqi and US troops have launched a major crackdown in Baghdad to curb rampant sectarian violence and have had some success in reducing the number of daily car bombings and shootings in the city.

The UN cut back many of its activities in Iraq after a truck bombing on its Baghdad headquarters in August 2003 that killed UN envoy Sergio Vieira de Mello and 21 others, and an attack on the International Committee of the Red Cross office.

Ban’s trip, the first by the top UN official since his predecessor, Kofi Annan, visited in November 2005, was staged with such secrecy that even his chief spokeswoman was unaware of it, UN officials in New York said.

It came against the backdrop of yet more violence. Three US soldiers were reported killedin Basra, Iraq’s second city whose oil fields are the source of most of the country's wealth.