Baghdad, Iraq (CNN) -- The series of explosions Saturday that killed dozens of people in Basra were caused by car bombs and roadside bombs, not by an accident, the U.S. military said Monday.
Basra's police chief had said over the weekend that the explosions were caused by a power generator. But the U.S. Forces-Iraq's deputy commanding general for operations, Lt. Gen. Robert Cone, told reporters Monday that the explosions were caused by two car bombs and two roadside bombs. They left 43 people dead and 103 wounded.
Cone called the attacks "a terrible incident," but added that they were not necessarily indicative of a larger trend. "I would like to point out that these are sporadic incidents," he said. "The fact is that we are working very hard with our Iraqi partners to make sure that they are working to address these type incidents and, by and large, we are very pleased with progress that they're making."
Cone expressed confidence that the transition to Iraqi forces will continue as planned. "Most of the units that are departing are already in the process of shipping out," he said, adding that the number of U.S. forces on the ground will not be much different after September 1.
Over the weekend the last U.S. combat brigade, the 4th Brigade of the 2nd Infantry Division, formally handed over combat operations to the Iraqi Army 6th Division. The soldiers of that brigade will be among the last to ship out as Operation Iraqi Freedom officially comes to an end at midnight on August 31 and Operation New Dawn, in which the remaining U.S. forces will be in an advise-and-assist role, begins.
Some senior Iraqi officials and civilians have expressed concern about a return to violence as the U.S. presence decreases.
But Iraq's ground forces commander, Lt. Gen. Ali Ghaidan, told reporters that his forces will be ready to assume the responsibilities all over Iraq when American forces pull out. "Between now and until the end of 2011, we will take over all the positions that are currently under the control of U.S. troops," he said. "Our forces are ready and capable to take over the security control."
"We're still very committed to Iraq," U.S. Army Gen. Ray Odierno, commander of U.S. Forces-Iraq, told CNN over the weekend. "We're still going to have 50,000 troops on the ground for a significant period of time to continue to help them [Iraqi forces] build that confidence."
At present, some 64,000 U.S. troops are in Iraq. In January 2009, 145,000 were there.
The number of U.S. military facilities in Iraq has dropped from 608 in 2007 to 112 last month and is on track to drop to 94 by September, Odierno said last month.
All U.S. combat forces are to be out of the country by December 31, 2011.
CNN's Arwa Damon and Mohammed Tawfeeq contributed to this story.