Syria's defence minister General Daoud Rajha was killed on Wednesday in a suicide bombing targeting the National Security headquarters in central Damascus, state television reported. Wednesday's attack struck the National Security building in Damascus during a meeting of Cabinet ministers and senior security officials. State-run TV said some of the officials were seriously wounded and later reported the defense minister killed. The capital has seen four straight days of clashes pitting government troops against rebels, who are trying to bring down the regime by force. The fighting is an unprecedented challenge to government rule in President Bashar Assad's seat of power. A suicide bomber attacked a security building in the heart of Damascus, Syria's state television reported on Wednesday as fighting raged across the capital for the fourth straight day. "A suicide attack has targeted the National Security building," the channel said of the security apparatus headed by General Hisham Ikhtiyar. The building is a heavily guarded headquarters in the city's central Rawda district. The attack came as battles raged across the city for the fourth consecutive day. There was no immediate news of Ikhtiyar's fate after the bombing. Born in 1941, Ikhtiyar is a key figure in the regime's repression of the 16-month revolt. On May 23 last year, the European Union added his name to the list of Syrian political figures targeted by sanctions. On May 20 this year, a reported attempt was made to poison Ikhtiyar and other key regime figures. A delivery boy was said to have added mercury to their food during a meal before fleeing.