UN chief Ban Ki-moon said Friday any use of chemical weapons by Syrian President Bashar al-Assad to combat the revolt would be an "outrageous crime".
"If it is the case, then it will be an outrageous crime in the name of humanity," Ban told a news conference after visiting a Syrian refugee camp in the Turkish border town of Islahiye.
He said "alarming news that the Syrian government has been preparing to use chemical weapons" was being received, adding however that none of the reports had been confirmed.
Ban's visit came amid international warnings to Assad's regime not to use chemical weapons to suppress the rebellion.
The UN chief, who flew to Turkey after visiting Jordan early Friday, repeated that he had written a letter to Assad urging him "not to use under any circumstances chemical weapons" and warning him that "it will create huge consequences."
The Syrian government has insisted that it would never resort to chemical weapons.
The United States says the use of chemical weapons in Syria is a redline for Washington and fears that battlefield advances by Syrian rebels could prompt the regime to use chemical arms, or such stocks could turn up in the hands of groups hostile to the United States and its allies.
On Monday, US President Barack Obama warned Assad of "consequences" if he used chemical weapons against his own people.
Ban's visit also comes a day after three-way talks between US Secretary of State Hillary Clinton, her Russian counterpart Sergei Lavrov and UN peace envoy to Syria Lakhdar Brahimi ended without any "sensational decisions".
Brahimi said all three agreed the situation was very bad in Syria during the surprise talks on the sidelines of an international gathering in Dublin.
Ban on Friday urged the international community not to "close your eyes while people are suffering" and stand united to end the crisis.
"I appeal to all sides particularly the Syrian government -- stop the killing. Stop the violence in the name of humanity," Ban told reporters.
"And I urge the international community and in particular the Security Council to stand united and act decisively to end the crisis."
Russia and China have blocked resolutions in the Security Council designed to put pressure on the Assad regime.