A car bomb has exploded in central Baghdad, injuring at least four people but reportedly causing no loss of life. The blast apparently targetted vehicles carrying security contractors working with the US.More than 60 people have been killed in the last three days, forming a sombre backdrop to an unannounced visit to the capital by NATO’s Secretary General Jaap de Hoop Scheffer. The worst violence was in Baquba, north of Baghdad, where a suicide attack on a police special division killed 10 officers and injured 26 other people. In other developments, US forces have announced they killed the man suspected of being al-Qaeda’s number two in Iraq on Sunday. They describe Abu Azzam as the second-in-command to Abu Musab al-Zarqawi, Iraq’s most wanted man.