Former Pakistan Minister Sheikh Rashid Ahmed was injured and four others were killed on Monday when unidentified gunmen attacked his election office in the garrison city of Rawalpindi.
Mr. Ahmed, who heads the Awami Muslim League, is a candidate for an upcoming by-election to a seat in the National Assembly.
The four persons who died were workers of the Awami Muslim League party. The injured party leader was taken to a nearby hospital, state-run media reported.
Mr. Ahmed, 59, was earlier a member of the opposition PML-Q and a close confidante of former President Pervez Musharraf.
Punjab Chief Minister Shahbaz Sharif directed authorities to conduct an immediate inquiry into the incident.
Mr. Ahmed served as the Federal Minister for Railways in Pakistan from 2006 to 2008 and had earlier held the portfolios of Labour and Manpower, Information and Broadcasting, Industries, Sports Culture, and Tourism and Investment.