An errant American rocket strike on Sunday hit a compound crowded with Afghan civilians in the last Taliban stronghold in Helmand province, killing at least 10 people, including five children, military officials said. Avoiding such civilian deaths, which came on the second day of a major allied offensive around Marja, has been a cornerstone of the war strategy by the top American commander, Gen. Stanley A. McChrystal. He apologized to Afghan President Hamid Karzai, saying, 'We deeply regret this tragic loss of life.' The strike came after American Marines and Afghan soldiers had been taking intense small-arms fire from a mud-walled compound in the area, American officers said. The answering artillery barrage instead hit a building a few hundred yards way, striking with a roar and sending a huge cloud of dust and smoke into the air. As the wind pushed the plume away, a group of children rushed outside. 'The compound that was hit was not the one we were targeting,' said Capt. Joshua Biggers, the commander of Company K, 3rd Battalion, 6th Marines, which had been engaged in a rolling gunbattle with Taliban insurgents throughout the day. It was unclear whether one or more rockets hit the building. Officers said the barrage had been fired from Camp Bastion, a large British and American base to the northeast, by a weapons system known as HIMARS, an acronym for High Mobility Artillery Rocket System. Its munitions are GPS-guided and advertised as being accurate enough to strike within a yard of their intended targets. McChrystal said in a statement that he was suspending use of the weapon system 'until a thorough review of this incident has been conducted.' There were conflicting reports about the number of dead in the strike. Daoud Ahmadi, the spokesman for Helmand province's governor, said in a telephone interview that 10 people had been killed. But American soldiers in the area said 11 civilians had died, and the joint military command, known as the International Security Assistance Force, put the toll at 12. Sunday was an intensive day of fighting around Marja, in an area of irrigated steppes and rural villages where a combined force of about 15,000 Afghan and foreign troops, led by American Marines, is now trying to break Taliban control. 