Major-General James Thurman said on Friday: "I would tell you I need more Iraqi security forces."
Thurman said that the Iraqi government had failed to supply six Iraqi army battalions - roughly 500 soldiers in each - to reinforce the streets of the capital.
"Baghdad's security hinges on the capabilities of the Iraqi security forces," Thurman said, arguing against moving more US soldiers to Baghdad.
Washington is counting on US-trained Iraqis to run security and let Americans start going home.
A spokesman for the Accordance Front party said its leaders met Nuri al-Maliki, the Iraqi prime minister, to urge protection for Sunnis after armed men attacked a Sunni area in Baghdad on Friday.
In Basra, where rival Shia factions are battling British forces and each other for control around Iraq's main oilfield, a rocket attack on the main foreign base in the southern city killed an American contractor working for the state department.
Meanwhile, a Danish soldier was killed in southern Iraq on Saturday after his patrol vehicle hit a bomb by the side of the road south of the city of Basra, the Danish central army command said.
"I can confirm that one Danish soldier was killed by a roadside bomb south of Basra when his vehicle, one of three travelling together, was hit," a Danish army spokesman told Reuters.
Another soldier was seriously injured in the same incident according to the same source.
Al-Maliki has vowed to use his new security forces to curb militias but it is unclear if he can make good on his promise