Early in the war, after the virtual destruction of the North Korean Air Force, U.S. Far East Air Force (FEAF) B-29 bombers carried out massive aerial attacks on transport centers and industrial hubs in North Korea. During this period, the official U.S. policy was to pursue precision bombing aimed at communication centers railroad yards and industrial facilities deemed vital to war-making capacity.
In early July 1950, General Emmett O’Donnell, Commander in Chief of Pacific Air Forces proposed to General Douglas MacArthur, Supreme Commander of Allied Powers, that the U.N. forces initiate firebombing methods such as those used against Japan toward the end of WWII.
MacArthur is said to have responded: “No… I’m not prepared to go that far yet. My instructions are very explicit; however, I want you to know that I have no compunction whatever to your bombing bona fide military objectives, with high explosives, in major industrial centers. If you miss your target and kill people or destroy other parts of the city, I accept that as a part of war.”
In September 1950, MacArthur reported to the United Nations, “The problem of avoiding the killing of innocent civilians and damages to the civilian economy is continually present and given my personal attention.”
In October 1950, FEAF commander General George Stratemeyer requested permission to attack the city of Sinuiju, a provincial capital with an estimated population of 60,000, over the widest area of the city, without warning, by burning and high explosives. MacArthur’s headquarters responded the following day: “The general policy enunciated from Washington negates such an attack unless the military situation clearly requires it. Under present circumstances, this is not the case.”

Despite the official precision bombing policy of UN forces, North Korea reported extensive civilian casualties.

The apparent contradiction between a policy of precision bombing and reports of high civilian casualties might be explained by the very low accuracy of bombing.

National Museum of the United States Air Force
According to a FEAF analysis, 209 bombs had to be dropped to reach an 80% likelihood of hitting a 20 by 500 foot target. Since many targets of the “precision” campaign were located in populated areas, high numbers of civilians were killed despite the policy of limited targeting.
Source: Wikipedia