BAGHDAD, Iraq (CNN) -- Violence in Iraq has fallen to its lowest level in almost two years, Defense Secretary Robert Gates said Wednesday.
The goal of stability in Iraq is "within reach," Gates said during a visit to Baghdad. But he cautioned patience as insurgent attacks have not stopped.
As he spoke, a car bomb attack in the capital killed 15 and wounded 32, an Iraqi Interior Ministry official said.
It was the latest in a series of deadly car bombs during his stay. And U.S. troops losses continued, with three soldiers reported killed in fighting on Tuesday.
But the secretary outlined the signs of progress that have been reported by the military in recent months, strides attributed in part to the U.S. military troop escalation called the "surge."
He said there's been "a decline in violence to levels not seen" since the bombing of the Askariya Mosque in Samarra in February 2006. That event sparked a wave of Sunni-Shiite sectarian violence.
Other examples of progress are a "substantial increase" in refugees returning to Iraq, rising international investment, and the thousands of Iraqi civilians who have been recruited to provide security help in neighborhoods.
"These positive developments have led to a growing sense of normalcy and hope," Gates said.
Many insurgents are believed to have migrated north, to places like Mosul, and while Gates said the challenges continue for troops in that area, he called the threats in that region now "less sophisticated."
"More than ever, I believe the goal of a secure and stable and democratic Iraq is within reach. We need to be patient and need to be resolved in desire to see signs of hope across Iraq flourish so all Iraqis can enjoy peace and prosperity," said Gates, who visited Iraq after stops in Afghanistan and Djibouti.
The three U.S. soldiers killed Tuesday were victims of "a complex attack" involving a bomb and small arms fire while they were conducting operations in Salaheddin province, the military said.
Since the start of the war in Iraq, the U.S. military has lost 3,886 troops, five during the month of December.
Meanwhile, a car bomb attack on the convoy of a top Iraqi general in Kirkuk on Wednesday left two people dead and the general among 11 wounded, a police official said.
In central Baquba, north of Baghdad, a car bomb explosion in a bus station killed five people and wounded 13 others Wednesday.
To the northwest in Mosul, an Iraqi civilian was killed and seven others were wounded in a car bomb explosion aimed at an Iraqi police patrol, police said. E-mail to a friend