"Efforts of the past three years did not bring any results. We have to raise new approaches that would be effective," Annan said.
Syria is currently being torn by the civil war that broke out in 2011, with the country's army fighting several opposition and rebel groups.
"To stop this, we have to have a common approach. We should refuse sending weapons, sending money to the militants or to the government unless we are together to stop the crisis," the former UN chief added.
According to the UN High Commissioner for Refugees (UNHCR), almost 4 million of Syrians have fled to Egypt, Iraq, Jordan, Lebanon and Turkey amid hostilities. Overall, nearly 200,000 people are estimated to have been killed in the conflict, according to the United Nations.
The Islamic State (IS) jihadist group is posing the most serious threat to Syria, as it has already managed to seize large parts of the country, as well as some territories in Iraq, continuously trying to make further advances.
