Following the action in Ruhengeri the RPF again began to wage guerrilla war. The Rwandan Army massed troops across the north of the country, occupying key positions and shelling RPF hideouts in the Virunga mountains, but the mountainous terrain prevented them from launching an all-out assault. Paul Kagame's troops attacked the Rwandan Army forces repeatedly and frequently, keen to ensure the diplomatic and psychological effect of the RPF's resurgence was not lost. Kagame employed tactics such as attacking simultaneously in up to ten locations across the north of the country, to prevent his opponents from concentrating their force in any one place. This low intensity war continued for many months, both sides launching successful attacks on the other, and neither able to gain the upper hand in the war. The RPF made some territorial gains including capturing the border town of Gatuna. This was significant as it blocked Rwanda's access to the port of Mombasa via the Northern Corridor, forcing all trade to go through Tanzania via the longer and costlier Central Corridor. By late 1991 the RPF controlled 5% of Rwanda, setting up its new headquarters in an abandoned tea factory near Mulindi, Byumba province. Many Hutu civilians in areas captured by the RPF fled to government-held areas, creating a large population of internally displaced persons in the country.