KABUL, Afghanistan (AP) — Defense Secretary Robert Gates today expressed “personal regret” for recent U.S. airstrikes that killed Afghan civilians, and pledged more accurate targeting in future.

After meeting with Afghan President Hamid Karzai and other senior government officials, Gates said at a news conference, “As I told them, I offer all Afghans my sincere condolences and personal regret for the recent loss of innocent life as a result of coalition airstrikes.”

Gates said the U.S. military takes extraordinary precautions to avoid civilian casualties, but added, “It is clear that we have to work even harder.” He told Afghan officials that he would be discussing the issue with American commanders and pilots today.

Later, Gates flew to Bagram, the main U.S. base in Afghanistan, and received a briefing on procedures for using air power.

Gates agreed to an Afghan government proposal to create a permanent joint investigative group to probe any incident involving civilian casualties, rather than assigning investigators to individual cases as they arrive, according to Pentagon press secretary Geoff Morrell.

Gen. David McKiernan, the commander of international forces in Afghanistan, said that a shortage of U.S. troops in Afghanistan is forcing commanders to rely more on air combat, which can cause more civilian deaths. The attacks that have angered and embarrassed the U.S.-backed Afghan government.

McKiernan said he needs at least three more combat brigades, in addition to the one arriving in January. Without the additional troops, the war will be longer and deadlier, he said.

“The danger is that we’ll be here longer and we’ll expend more resources and experience more human suffering than if we had more resources placed against this campaign sooner,” McKiernan told reporters traveling with Gates.

He also said he knows he can only get more combat forces if troops are diverted from Iraq. The Army brigade arriving in Afghanistan in January was initially scheduled to go to Iraq, and it includes about 3,700 soldiers.

McKiernan said his Washington bosses had “validated” his request for the three additional brigades — or at least 10,000 more troops — and said he believes it is a question of when, not if, he will get those reinforcements. There currently are about 33,000 U.S. troops in Afghanistan.

The wars in Afghanistan and Iraq are headed in opposite directions: Violence is down substantially in Iraq and U.S. troop levels are declining, while the fighting is heating up in Afghanistan and more U.S. troops are needed.

McKiernan said that while he does not believe the U.S. is losing the war there, “we are winning slower in some places than others.”

There have been a series of attacks in Afghanistan that resulted in civilian deaths — most notably the highly publicized allegations that a U.S. attack on an Afghan village compound on Aug. 22 killed as many as 90 Afghan civilians, including women and children. The U.S. military has disputed the allegation but also has opened a new investigation in light of emerging evidence.