The flare-up in violence in Shiite areas of southern Iraq and Baghdad has yet to alter U.S. plans to withdraw more combat forces this spring, Defense Secretary Robert Gates said Monday.

Gates, speaking to reporters traveling with him from Brussels, Belgium, to the Danish capital, offered a mildly upbeat assessment of the Iraqi government's military intervention in the southern Iraqi city of Basra.

He said Iraqi Prime Minister Nouri al-Maliki is to be commended for taking the initiative in Basra, and he described the Iraqi security forces as having performed reasonably well, with American support.

"Based on what I've seen, the limited reporting I've seen ... they seem to have done a pretty good job," Gates said without mentioning that al-Maliki had promised a "decisive and final battle" for control of the southern oil capital of Basra when he ordered a military intervention there a week ago.

"We've all known that at some point the situation in Basra was going to have to be dealt with," Gates said. "It is the economic lifeline of the country and been under the control of a bunch of thugs, gangs (and) militias. Over the long term it's unacceptable."

The clashes in Basra coincided with a surge in violence in parts of Baghdad, including the Sadr City area that is heavily Shiite. Rocket and mortar attacks on the protected Green Zone that houses the U.S. Embassy and Iraqi government offices are believed to have originated in some cases from Sadr City.

Gates was asked whether the higher levels of violence might change the plan to continue withdrawing Army brigades from Iraq this spring. Of the five extra brigades that President Bush ordered to Iraq last year, two have departed and the other three are scheduled to go home between April and the end of July.

"I have not heard anything along those lines," Gates said, adding that there would be "more finality" to that question when Gen. David Petraeus, the top U.S. commander in Iraq, returns to Washington to report to Congress on April 8.

"I have not heard or seen anything that would indicate a need to change" the pullout plan, Gates said.

There are now 158,000 U.S. troops in Iraq. By the end of July that number is supposed to fall to 140,000. Whether additional troops are withdrawn after July is one of the questions that Petraeus is expected to address in his testimony; he has already made it known that he wants a "period of assessment" for at least several weeks after July before deciding on the timing of further withdrawals.