Mr Ban was speaking at UN headquarters in New York alongside US Secretary of State John Kerry.
Both men stressed the urgency of finding a political solution to the conflict. Mr Ban appealed for fresh efforts to convene a peace conference.
A further 1.7 million Syrians have been forced to seek shelter in neighbouring countries.
The UN announcement came as reports from the capital, Damascus, said that seven people had been killed in a car bomb attack.
Syrian state media said the attack took place in the suburb of Jaramana, home to many Christians and Druze, adherents of a heterodox offshoot of Shia Islam. There has tended to be more support for President Bashar al-Assad within those communities.
"The military and violent actions must be stopped by both parties and it is thus imperative to have a peace conference in Geneva as soon as possible," Mr Ban said, according to AFP.
Previous attempts at holding a peace conference have been delayed by differences between international powers, particularly Russia and the US, and doubts about whether all sides from Syria would attend.
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