UN chief Ban Ki-moon said Friday any use of chemical weapons by Syrian President Bashar al-Assad's regime to combat the revolt would be an "outrageous crime," amid growing fears it might resort to them to stay in power.
"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 may be 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, including from US President Barack Obama, 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."
During a visit to Baghdad on Thursday, Ban said Assad should be "brought to justice" if his regime uses chemical weapons against the rebels.
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 red line for Washington and fears that battlefield advances by Syrian rebels could prompt the Assad 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, Obama warned Assad of "consequences" if he used chemical weapons against his own people.
Ban's visit 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.
The meeting came on the heels of Russian President Vladimir Putin's talks with Turkish Prime Minister Recep Tayyip Erdogan early this week in Istanbul.
"I have taken note" of the Istanbul summit where the two leaders discussed "new ideas" on how to respond to the Syrian crisis, Ban told reporters in Ankara.
He hoped that the new strategies would be very closely coordinated with Brahimi and the other key parties concerned, "so that there will be a consensus of views among the international community."
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Putin and Erdogan discussed their opposing views and agreed to disagree on Syria at Monday's talks but Russia has distanced itself from Assad and Putin said Russia's leaders were not "inveterate defenders" of the current regime in Syria.
In Ankara, Ban met with Turkish President Abdullah Gul, Erdogan and Foreign Minister Ahmet Davutoglu.
Ban earlier 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 at the Islahiye camp housing some 8,500 refugees.
"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.
Ban also denied that there were discussions about organising safe passage from Syria for Assad and his family.
"This is the issue on which the international community has not yet started to discuss," said the UN chief.
"What I am saying is that first and foremost the violence must stop then the political dialogue must start as soon as possible."
The Syrian crisis has also affected regional countries including Turkey, Lebanon and Jordan which have received an influx of refugees as the war between Assad's loyalist troops and rebel forces continues.
"We have seen tripling refugee numbers since July and the numbers keep growing," Ban said without elaborating.
"And I'm afraid that any serious escalation of violence in Syria will lead to a dramatic increase in refugee numbers."
He also commended the Turkish government's "open-door policy receiving all the refugees fleeing Syria without condition."
Ban urged the international community to extend financial support to countries hit by the refugee exodus, noting that Turkey alone spent almost one billion dollars.
Since the uprising against Assad first erupted in March 2011, more than 135,000 Syrians have crossed into Turkey, according to official figures provided by the government. But the actual number is likely to be much higher if it includes Syrians living outside the camps.