Countries that want to reopen embassies in Damascus or resume ties with Syria's government must end their support for Syria's rebels, President Bashar al-Assad said on Sunday.
"We are not isolated like they think, it's their arrogance that pushes them to think in this manner," said Assad in a speech to members of Syria's diplomatic corps carried on state television.
"There will be neither security cooperation, nor the opening of embassies, nor a role for certain states that say they want to find a way out (of Syria's war), unless they explicitly cut their ties with terrorism," he added.
The United States and most European countries shut their embassies in Damascus after the government's bloody crackdown on protests that erupted in March 2011.
Ties have remained severed throughout the brutal civil war that followed, which has since killed more than 330,000 people.
But in recent months there have been reports that Western countries could be seeking to quietly resume ties.
In May, the pan-Arab newspaper Al-Hayat reported that French President Emmanuel Macron was considering revisiting the decision to shutter Paris's embassy, though the Quai d'Orsay denied it.
France has been a leading backer of the Syrian opposition since 2011, and has regularly called for Assad's departure.
Assad's government has recovered large swathes of territory from rebels and jihadists in recent months, its advances enabled by the start in September 2015 of a Russian military intervention to bolster regime troops.