Col. Abdul Hanan, the acting provincial police chief in Afghanistan's eastern Khost province, said the fighting broke out after Pakistani forces crossed into Afghanistan.
Two officials of the Frontier Corps (FC) were martyred and five injured in a cross-border attack in Kurram Agency, the Inter Services Public Relations (ISPR) said on Sunday.
Kurram Agency is one of the most sensitive tribal areas of Pakistan as it shares the border with three Afghan provinces. Soon after the attack, announcements were made through mosques' loudspeakers in various villages, situated along the Pak-Afghan border. Pakistani troops are exercising maximum restraint so as to avoid any Afghan civilian casualties. "Mil [military] engagement is underway to defuse situation", the ISPR said in a statement.
Pakistan began fencing the Pak-Afghan border previous year to prevent terrorists from crossing into the country from Afghanistan.
Clashes are frequent in the area as Afghanistan doesn't recognize the 2,400-kilometer Durand Line (drawn by Britain in 1896) as its worldwide border with Pakistan.
Clashes are still underway, he said.
The bodies of the two Pakistanis were found on the Afghan side of the border near Pakistan's tribal belt, Zadran told AFP. He claimed that the Afghan forces have also captured Pakistani soldiers, but refused to reveal their number.
Afghan officials often give conflicting casualty figures.
Local administration told media that the attack was carried out from the Khost province of Afghanistan at the personnel deployed at a post in Laka Tika area of Kurram Agency.
Islamabad rejects the accusation, countering that Islamist militants targeting Pakistani forces and civilians reside on the Afghan side of the border.