Petraeus will take over as the new head of Central Command (Centcom) in late October, a role which involves taking responsibility for US troops from the Horn of Africa to Central Asia.
He will be responsible for overseeing US military strategy in Afghanistan and Iraq, Boylan said.
'Surge' support
Petraeus's new role comes amid calls for US troop levels to be increased in Afghanistan, amid rising violence in that country.
He was approved by the US senate to head Central Command after Admiral William Fallon stepped down from the role in March.
Before leaving Iraq, Petraeus will offer to George Bush, the US president, his recommendations on troop cuts in Iraq.
There are about 144,000 US troops in Iraq but fighting in the country has dropped to its lowest level in four years.
Petraeus has commanded US troops in Iraq since February 2007 and has been credited by the Bush administration with improving Iraqi security through a so-called “surge” of 30,000 troops.
He masterminded a counter-insurgency strategy that emphasised the importance of respect towards Iraqi citizens by US soldiers.
Those same forces were ordered to pursue al-Qaeda and other groups blamed for destabilising Iraq.
Washington has since withdrawn five combat brigades that were deployed as part of the surge, amid improvements to security across Iraq.
On Thursday, in an interview with the Financial Times, Petraeus said that US combat troops could be out of Baghdad by July 2009.
He told the newspaper that Iraq is a "dramatically changed country" possessing a "degree of hope that was not present 19 months ago".
But he warned that the unresolved status of the northern oil city of Kirkuk, persistent sectarian tensions, and al-Qaeda still posed challenges to long-term stability.