At least four people were killed and four others were wounded in multiple blasts targeting security personnel in Pakistan's southern city of Karachi on Wednesday.Three bomb blasts, including a suicide attack, killed at least four people, including three paramilitary rangers and a private security guard, according to police officials.Two improvised explosive devices were placed close to a rangers' checkpoint in the busy North Nazimabad neighbourhood, killing one soldier and wounding three, said senior police officer Amir Farooqi.In another incident, a suicide bomber blew himself up at the entrance of a rangers' headquarters, killing two soldiers and a civilian security guard and wounding another.The suicide bomber had tried to force his way into the premises before blowing himself at the gate as guards were trying to apprehend him.Karachi, a city of 18 million people and which contributes 42 per cent of Pakistan's GDP, has been a target of militant insurgency, sectarian violence, gang wars and abductions.