ISLAMABAD, Oct. 17 (Xinhua) -- The United States shifted hundreds of its troops to the Afghan area bordering North Waziristan on Sunday along with heavy arms and gunship helicopters and sealed the Pak-Afghan border for all types of movement. Tribesmen living in the border areas said Afghan and U.S. authorities had clamped a curfew in the Gurbaz area of Afghanistan 's Khost province and started house-to-house searches. The abrupt deployment of U.S. forces near the border area with Pakistan has escalated tension in the militancy-plagued North Waziristan tribal region as U.S. forces immediately sealed the main Ghulam Khan- Khost highway...