SOUTH WAZIRISTAN - At least four Pakistani soldiers were killed and two others sustained injuries when mortar shells fired from across the border hit a check post in South Waziristan Agency on Tuesday. Sources said around three mortar shells fired from Afghanistan hit a security check post in Angoor Adda in South Waziristan. As a result, four security personnel were killed on the spot, while two others sustained injuries. The check post was completely destroyed in the attack. Officials said more than 20 mortar shells were fired from across the border and three of them slammed into a paramilitary forces check post. In recent weeks, tensions have sharply risen on the border between Pakistan and Afghanistan, as Islamabad has blamed Kabul for attacks inside Pakistani territory in which many people, including security men, have been killed. Agencies add: Officials on Tuesday accused the Afghan army of firing mortar bombs across the border, killing four Pakistani soldiers and stepping up a recent surge of cross-border violence. Four soldiers were killed and two others were wounded in this cross-border attack, a security official in Peshawar told AFP, saying that the shelling continued for around two hours. More than 20 mortar shells were fired from across the border. Three shells slammed into a paramilitary Frontier Corps checkpost in Angoor Adda, he added. Another security official in Wana, the main town in South Waziristan, confirmed the incident and casualties. Both officials blamed the Afghan army for the attack. The incident sparked panic among the locals. They staged a protest and chanted slogans against Afghan National Army for targeting cross-border attacks.