George Bush, the US president, is seeking to send 21,500 extra troops, most of them to Baghdad, to help the government of Nuri al-Maliki, the prime minister, secure the capital and the western province of Anbar.
Petraeus, a veteran of two tours of Iraq and a counter-insurgency expert, has called for the additional American troops to be deployed as quickly as possible.
Thousands of US and Iraqi troops began a security crackdown in the capital earlier this week.
"The rucksack of responsibility is very heavy ... we will all have to share the burden and move forward together," Petraeus told his audience at Camp Victory, a US base on the outskirts of the capital.
During his time as commander of the US 101st Airborne Division in 2003, he won plaudits for working closely with local leaders to improve security in the northern city of Mosul.
He also led the effort to train Iraqi security forces and his counter-insurgency manual emphasises the importance of understanding local politics and culture, two things which could be vital in achieving success.
Some Iraqis have said one of the most positive developments of the new strategy is al-Maliki's commitment to target both Sunni and Shia fighters.
Hoda Abdel Hamid, Al Jazeera's correspondent in Baghdad, said: "Many Iraqi officials ... pointed out that the most important thing could be the new attitude of al-Maliki who has convinced Sunni leaders ... he is extremely serious about going after anyone who is holding a weapon outside the law."
Petraeus, who has a doctorate in international relations, took over the command from US general George Casey.
Ahead of the ceremony, the outgoing commander said: "My greatest fear is that the Iraqis can't put the past behind them.
"We liberated them from 35 years of tyranny. We can't liberate them from the fears and prejdices that grew up in that 35 years. They have to do that themselves," Casey said.
Shortly before Petraeus took command, armed men stormed into two houses south of Baghdad, killing three members of one family and wounding two of their neighbours, police said.
Eight attackers drove up in three cars before killing a man, his wife and their 23-year-old daughter in one house in Musayyib, 60km south of Baghdad. They then attacked a second house, wounding a husband and wife.
|"We liberated them from 35 years of tyranny. We can't liberate them from the fears and prejdices that grew up in that 35 years" |
General George Casey, outgoing US commander in Iraq
A car bomb also exploded in the mainly Shia area of Karradah in central Baghdad, killing at least five people and wounding 10, including three policemen, police said.
US troop deaths
The US military on Saturday announced three more American soldiers had died in an explosion in volatile Diyala province northeast of Baghdad.
The blast occurred as Task Force Lightning soldiers searched for a weapons cache near Baqouba. US and Iraqi forces have battled Sunni fighters and Shia militias in Diyala for months.
Also on Saturday, dozens of Shias and a handful of Sunnis gathered for the reopening of a Sunni mosque in Baghdad's Shia militia stronghold of Sadr City.
Local officials said they hoped to encourage members of the displaced Sunni minority to return to the district as part of reconciliation efforts.