There were also units formed by Caucasian and Rumelian Turks, who took part in the battles in Mesopotamia and Palestine. Among Ottoman forces, volunteers were not only from Turkic groups; there were also smaller numbers of Arab and Bedouin volunteers who fought in the campaign against the British to capture the Suez Canal, and in Mesopotamia. Volunteers were considered unreliable by the organised army, due to a lack of training and a perception of mainly mercenary interests from the Arab and Bedouin volunteers. Heavy fighting also placed pressure on the Ottoman volunteer system.