Damascus is warning Washington not to conduct air strikes on militants inside its territory without its consent.
Syrian Foreign Minister Walid al-Muallem said in Damascus on August 25 that an act "by anyone" without his government's approval would be considered aggression.
But Muallem also said Syria is ready to work with the international community in fighting Islamist terrorists.
The remarks are the first response by a senior Syrian official to U.S. air strikes on Islamic State fighters in Iraq near Syria's border.
German Foreign Ministry spokesman Martin Schaefer said in Berlin that Germany had no plans to resume ties with Damascus because of the Islamic State threat.
Syria has often sought to rally support in its war against opposition groups by dubbing it part of the global war on terror.