ROME, Dec 9 (Reuters) - Violence in Iraq has in the past few weeks fallen to its lowest level since summer 2003 and security gains, while still at risk of reversal, are less fragile than before, U.S. General David Petraeus said on Tuesday.

Petraeus, who leads the U.S. Central Command, said the past two weeks in particular had shown impressive gains for security in Iraq.

"I think that no one disputes at this point that there has been anything but very significant progress in Iraq," he said, addressing a gathering at the American Studies Centre in Rome.

"The situation, despite this progress, does remain fragile and it is reversible, but it is less fragile than it was, for example, when ... I last testified before the U.S. Congress back in May."

U.S. President-elect Barack Obama has said he believes U.S. combat troops could be withdrawn from Iraq in 16 months.

Petraeus was the top U.S. commander in Iraq from February 2007 to September 2008.

Leading Central Command since Oct. 31, he oversees U.S. military operations and strategy in a volatile swathe of the world that covers 20 countries, from the Middle East to Central and South Asia, including Iraq and Afghanistan. (Reporting by Phil Stewart, editing by Tim Pearce)

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