AP, REUTERS - Syria's foreign minister warned the United States on Monday not to conduct airstrikes inside Syria against the Islamic State group without Damascus' consent, saying any such attack would be considered a violation of sovereignty and an aggression.

Walid al-Moallem said such an act "by anyone," without the approval from President Bashar Assad's government, would be a violation of Syrian sovereignty and would be considered an aggression.

But the top Syrian diplomat also said on Monday that Syria is ready to work with regional states and the international community in the war on terror amid the onslaught of Islamic militants.

Al-Moallem's remarks at a press conference in Damascus marked the first public comments by a senior Assad official on the threat posed by the Islamic State, which has captured large swaths of Iraqi and Syrian territory.

Al-Moallem denounced the Islamic State's killing of U.S. journalist James Foley.

Also on Monday, the German Foreign Ministry said Germany has no diplomatic contacts with the Assad government and no plans to rekindle ties because of the threat posed by the militant group Islamic State.

"The regime of President Assad has committed unbelievable injustice in every form during the civil war that has been raging for 3-1/2 years. Nearly 200,000 people have died," Martin Schaefer, a spokesman for the German foreign ministry told a government news conference.

"To be honest it is very difficult to imagine that all this can be ignored in the name of Realpolitik, that one says, now we have ISIS, which is worse than Assad, so now we have to get into bed with the one that isn't quite so bad," he added.

"This is too simple. I am not aware of any thoughts or deliberations, whether in the fight against ISIS or otherwise, about working with the regime of President Assad," Schaefer said. "I am not aware of any political or diplomatic contacts between Germany and the Syrian government."