Until 1967 the FRELIMO showed less interest in Tete region, putting its efforts on the two northernmost districts of the country where the use of landmines became very common. In the region of Niassa, FRELIMO's intention was to create a free corridor to Zambézia. Until April 1970, the military activity of FRELIMO increased steadily, mainly due to the strategic work of Samora Machel in the region of Cabo Delgado. In the early 1970s, after the Portuguese Gordian Knot Operation, the nationalist guerrilla was severely damaged.