BEIRUT — A new wave of airstrikes targeting the Syrian city of Raqqa, the headquarters of the extremist Islamic State group and the focus of an international military campaign, killed at least eight people, including five children, Syrian opposition groups said Friday. The strikes came as France’s foreign minister, Laurent Fabius, declared that destroying the headquarters of the Islamic State, also known as ISIS or ISIL, and “neutralizing and eradicating” the extremist group is the main objective of the international campaign. A Raqqa-based activist group that reports on ISIS, known as Raqqa is Being Slaughtered Silently, said Friday that most of the casualties in the latest aerial bombardment occurred when warplanes targeted the city’s Heten School.