In May 1977, General Walls received intelligence reports of a ZANLA force massing in the town of Mapai, in the neighbouring country of Mozambique, and he launched an attack across the border to remove the threat. At this time Walls briefed the press that the Rhodesian forces were changing tactics from "contain and hold" to "search and destroy", and adopting a military policy of "hot pursuit when necessary." On 30 May 1977, a force of around five hundred Rhodesian troops crossed the border into Mozambique (which had only gained independence from Portugal in 1975), engaging the enemy with support from the Rhodesian Air Force (RhAF), and paratroopers conveyed in Second World War-era C-47 Dakotas. At the end of the operation, General Walls announced that it had killed 32 guerrillas for the loss of one Rhodesian pilot in action. Mozambique's government disputed the number of casualties, stating it had shot down four Rhodesian aircraft and taken several Rhodesian prisoners of war, which the Rhodesian government denied. Walls announced a day later that the Rhodesian Army would occupy the captured area of Mozambique until it had removed nationalist guerrillas from it. Kurt Waldheim, the Secretary-General of the United Nations, condemned the incident on 1 June, and political pressure, led by the United States, prompted the Rhodesian government to order its forces out of Mozambique.