On June 10, 1970, a major counter-offensive was launched by the Portuguese army. Operation Gordian Knot (Portuguese: Operação Nó Górdio) targeted permanent insurgent camps and the infiltration routes across the Tanzanian border in the north of Mozambique over a period of seven months. The operation involved some 35,000 Portuguese troops,[35] particularly elite units like paratroopers, commandos, marines and naval fusiliers.[66]


Portuguese soldiers on patrol, illustrating the difficult terrain they encountered
Problems for the Portuguese arose almost immediately when the offensive coincided with the beginning of the monsoon season, creating additional logistical difficulties. Not only were the Portuguese soldiers badly equipped, but there was very poor cooperation, if any at all, between the FAP and the army. Thus, the army lacked close air support from the FAP. Mounting Portuguese casualties began to outweigh FRELIMO casualties, leading to further political intervention from Lisbon.

The Portuguese eventually reported 651 guerrillas as killed (a figure of some 440 was most likely closer to reality) and 1,840 captured, for the loss of 132 Portuguese soldiers. Arriaga also claimed his troops destroyed 61 guerrilla bases and 165 guerrilla camps, while 40 tons of ammunition had been captured in the first two months. Although "Gordian Knot" was the most effective Portuguese offensive of the conflict, weakening guerrillas to such a degree that they were no longer a significant threat, the operation was deemed a failure by some military officers and the government.