 A bomber hit a bank in Kirkuk as soldiers collected their pay |
Military spokesman Maj Gen William Caldwell said there had been a "disheartening" 22% rise in attacks in Baghdad since the end of last month.
His comments came as a wave of bombings across Iraq killed at least 41 people.
President George W Bush has said the surge in Iraq may be equivalent to the US experience in the Vietnam War.
Mr Bush acknowledged that the escalation of violence "could be" comparable to the 1968 Tet Offensive against US troops, which helped turn public opinion against the Vietnam War.
But, speaking on ABC News, Mr Bush denied that the rising number of Iraqi and US military deaths in Iraq meant the campaign there was failing.
Deadly month
Launched in June, Operation Together Forward is a joint US and Iraqi security drive in which thousands of extra troops have been deployed in Baghdad.
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But Gen Caldwell said attacks on US troops and Iraqi forces in Baghdad has risen significantly in the first three weeks of the Muslim holy month of Ramadan, which began in the last week of September.
"Operation Together Forward has made a difference in the focus areas but it has not met our overall expectations of sustaining a reduction in... violence," he said.
Gen Caldwell said 73 US soldiers had been killed so far in October, which was heading towards becoming the deadliest month for US forces in Iraq for two years.
The senior US commander in Iraq, Gen George Casey, has now ordered a review of the strategy.
The gloomy assessment by the US military will add to growing pressure on the Bush administration for some shift in strategy in Iraq, says the BBC's James Westhead in Washington.
But the White House dismissed reports that it was preparing for a change of course, with spokesman Tony Snow describing them as a "bunch of hooey".
Curfew
The US comments came on another day of violence in Iraq. In Mosul in the north there were six separate suicide bomb attacks on Thursday alone.
In the deadliest attack, an explosives-laden fuel lorry blew up at a police station in the city.
Civilians bore the brunt of the attack, as many of the casualties were motorists waiting to buy fuel at a nearby petrol station.
Shortly after the blast, insurgents fired mortars and small arms and triggered more explosions in Mosul, killing at least three more people.
The violence prompted authorities to impose a six-hour curfew until calm was restored.
Correspondents say Mosul has witnessed a recent escalation of violence, with Sunni Arab insurgents battling US troops and the Shia-led government in Baghdad.
Attackers also struck in Kirkuk, killing 12 more people and wounding 70 when a car bomber targeted a crowded bank.
The blast tore though a crowd of soldiers who had gathered there to collect their salaries.
Elsewhere, at least 10 people were killed when a roadside bomb ripped through the Shia market town of Khalis.
Meanwhile, police in Baghdad said at least two officers and two passers-by were killed in the south of the city after a double roadside bomb attack on a police patrol.
