About eighteen mortar shells fired from Afghanistan fell in Pakistan's border area in North Waziristan tribal agency late Friday but no damage was reported, said reports here on Saturday. Pakistani security forces retaliated by firing 29 mortar shells in the direction from where the mortar shells came from Afghanistan, citing official and security sources local media reported. There was no report of any human or material losses in the Afghan territory as a result of the action, it said. Sources said shells fired from across the border have landed in the Pakistani territory twice in the past 24 hours. During the night, three shells were fired at the Bangidar area in Ghulam Khan district. About 10 hours later, around 15 shells apparently fired by US-led coalition forces and Afghan army targeted the Wai post manned by Pakistani security forces in Ghulam Khan. The shells landed near the post but did not cause any damage. It was at this stage, said sources, that Pakistani forces were provoked to fire in retaliation. They fired 29 shells towards the Afghan territory, sources said. The incident occurred three days after four mortar shells were fired from the Afghan side in Muqbal Ghuzgarhi area in Kurram tribal agency near the Pak-Afghan border. These mortar shells were fired from the Paktia province in Afghanistan into Pakistani territory, which caused no loss of life or damage to property.