The United Nations has adopted a resolution supporting efforts by Russia and Turkey to end violence in Syria and start peace negotiations.
Russia and Turkey announced the ceasefire this week, the third truce this year seeking to end the nearly six years of war in Syria.
Peace talks between President Bashar al-Assad's government and rebel forces in Syria are set to take place next year in Kazakhstan.
Syrian rebel groups have said that they would consider a ceasefire deal brokered by Russia and Turkey "null and void" if government forces and their allies continued to violate it.
Airstrikes and clashes have continued in some areas since the ceasefire officially began on Friday.
A statement signed by a number of rebel groups said: "Continued violations by the regime and bombardment and attempts to attack areas under the control of the revolutionary factions will make the agreement null and void."
The Democratic presidential candidate may also have shown his cards on his choice of running mate.
The US president also shared a post on Twitter accusing Dr Anthony Fauci of misleading the public over hydroxychloroquine.
Fears over an impending second wave of coronavirus dominates Wednesday’s front pages.