The Syrian conflict "has become a cancer on a global scale", incoming UN Secretary General Antonio Guterres has said, while hoping Washington and Moscow overcome their differences to help end the crisis.
The war has caused "not only the suffering of the Syrian people" but also sparks "violent reactions which in some cases lead to terrorist acts", the former Portuguese premier told Portugal's SIC television channel in an interview broadcast on Wednesday.
The conflict began in 2011 as an uprising against President Bashar al-Assad but quickly morphed into a civil war after the regime unleashed a brutal crackdown against dissent.
The war has killed more than 310,000 people and forced millions more to flee their homes.
It has since become a complex, multi-front conflict, drawing in global powers as well as militias and jihadists.
While Western powers and some regional states have backed the rebellion, Russia and Iran have thrown their full weight behind Assad's regime.
Guterres termed the conflict a "global threat" and said global powers must decide to end the conflict, something he judged could not be done without external support.