but Mao Zedong and his colleagues ardently refused; as a result, the United Nations General Assembly passed Resolution 498 on 1 February, condemning China as an aggressor, and demanded that its forces withdraw from Korea. UN counteroffensives The UN Command, under new commander Matthew Ridgway, began counterattacks in late January 1951 that retook Seoul from the PVA/KPA on 16 March and brought the fighting to the hills situated along the 38th Parallel. PVA commanders launched a counterattack in mid-February, with their Fourth Phase Campaign, but after gaining ground, this too was halted by UN troops in the Battle of Hoengsong and the Battle of Chipyong-ni. The PVA by this time had been badly mauled, and were worn out from incessant combat and exhaustion and their supply lines had been constantly bombed, further weakening their fighting capabilities due to lack of food and supplies. In mid-April 1951 UN forces in the central front in Korea were engaged in Operation Dauntless to advance UN positions from the Kansas Line north of the 38th Parallel to positions north of the 38th Parallel designated the Wyoming Line which would threaten the PVA/KPA logistics hub marked out by the towns of Pyonggang, Ch'orwon and Kumhwa named the Iron Triangle. The advance by US I and IX Corps was to menace the Triangle, not invest it and if struck by strong enemy attacks during or after the advance, the two Corps were to return to the Kansas Line. US Eighth Army intelligence on 18 April warned that a PVA/KPA attack was likely any time between 20 April and 1 May but on 21 April Eighth Army commander General James Van Fleet decided to continue the Dauntless advance. I Corps' final Dauntless objectives lay in the zones of the US 25th and 24th Infantry Divisions stretching north of the Utah Line (which arched above Kansas between the Imjin River and the eastern slopes of Kungmang Mountain, its trace resting on the prominent Kumhak, Kwangdok and Paegun mountain masses) to Ch'orwon and Kumhwa at the base of the Iron Triangle. Leading the IX Corps' advance were the ROK 6th Division and the US 1st Marine Division. In their sector the Wyoming Line curved southeast from the Kumhwa area to the Hwacheon Reservoir. On 21 April the two divisions moved above the Kansas Line against almost no opposition. Immediately west, the 24th Division did not test the opposition below