Sardar Sooran Singh, the Special Assistant to Chief Minister Khyber Pakhtunkhwa, was assassinated in Pir Baba area of Buner district.
Nine candidates on Wednesday filed nominations for Pakistan's presidential election, with the ruling Pakistan Muslim League-Nawaz's India-born nominee Mamnoon Hussain emerging a clear frontrunner for the poll to be held on July 30.
Pakistan will hold the next presidential election on September 6, two days before the end of the term of incumbent President Asif Ali Zardari.
Sharif said that Khan's position was much weaker this time than in 2013 when last general elections were held.