The US military said on Sunday a recent increase in bombings was not the start of a wider trend in Iraq and violence had decreased overall. US military spokesman Rear Admiral Greg Smith said he did not think recent security gains were being reversed.
"I would not look at the last few weeks as an increase or a trend, but there has been a sporadic series of events that ... have resulted in significant loss of life," Smith told a news conference.
Smith said the spate of recent attacks needed to be compared with a year ago, when thousands of civilians were dying in sectarian violence between majority Shi'ites and minority Sunni Arabs, with US troops also suffering heavy casualties.
Iraqi police said 68 people died when two bombs exploded within minutes of each other in a popular, crowded shopping area in central Baghdad on Thursday evening, the deadliest single bombing in the capital since last June. Overall levels of violence are sharply down since last June, when 30,000 extra US soldiers were deployed.
That coincided with a ceasefire by Shi'ite cleric Moqtada al-Sadr's Mehdi army militia and a decision by mainly Sunni Arab tribal sheiks to turn against Sunni Islamist al Qaeda.
But the number of violent civilian deaths rose sharply in February, the first increase in six months, after bombings which Smith blamed on al Qaeda killed more than 160 people.
Any upsurge in violence could pose headaches for Washington over its plans to withdraw some US troops from Iraq. Five of 20 combat brigades in Iraq are due to be pulled out by July 31, reducing the overall US military presence from about 160,000 to around 140,000.
On Thursday, the US military said the second of the brigades would be returning from Baghdad, while another based in the city was also earmarked for withdrawal.
ROGUE MILITIAS:
"There has been substantial progress-levels of violence are down by 60-70 percent, civilian deaths and a variety of other categories that we watch are all down," General David Petraeus, the US military commander in Iraq, told Sky News.
US commanders say al Qaeda is the greatest threat to Iraq's security but they are also concerned about "rogue" Shi'ite militias which they accuse Iran of financing, training and arming.
Tehran has denied the charges, blaming the US presence in Iraq for the violence.
Smith said there was clear evidence that "elements from inside Iran" were backing militias in Iraq, saying captured fighters had confirmed their accusations and US forces regularly found caches containing Iranian-made weapons.
Iranian, US and Iraqi officials held three round of talks in Baghdad last year on ways to end the violence, easing a diplomatic freeze between Washington and Tehran. But a fourth rounds of talks has been repeatedly delayed with Washington and Tehran blaming each other for the impasse.