| ISLAHIYE, Turkey
ISLAHIYE, Turkey U.N. Secretary-General Ban Ki-moon said on Friday he had not received any confirmed reports that Damascus was preparing to use chemical weapons, but said it would be an "outrageous crime" if it did so.
Several Western countries have this week warned President Bashar al-Assad's government not to resort to chemical arms, with many citing intelligence which Washington said showed Assad might be preparing to use poisonous gas.
Damascus has said it would never use chemical weapons against its own people, saying the reports were designed to whip up support for international intervention in Syria. Washington has said the use of chemical weapons would cross a "red line".
"Recently, we have been receiving alarming news that the Syrian government may be preparing to use chemical weapons. We have no confirmed reports on this matter," U.N. chief Ban said after visiting a Syrian refugee camp in Turkey.
"However, if it is the case, then it will be an outrageous crime in the name of humanity ... I know that many world leaders have added their voices urging him not to use it and warning him that it will create huge consequences," he said.
Ban's comments came as rebels fighting to topple Assad declared Damascus International Airport a battle zone on Friday, while Moscow and Washington both sounded glum about the prospects of a diplomatic push to end the conflict.
Ban, who has warned Assad twice over chemical weapons use in writing, said he had also spoken on Thursday with the head of the Organization for the Prohibition of Chemical Weapons about ways to investigate the reports but no concrete plan had emerged.
Opposition forces and Western intelligence officials have said recent rebel advances - including around the capital Damascus - may provoke Assad into using chemical weapons, which he is widely believed to possess.
Assad blames the West and its Gulf Arab allies, who have thrown their weight behind the opposition, for the unrest in Syria that rebels say has killed 40,000 people. Damascus says the uprising is led by "terrorists" guided from abroad.
"SLOW INTERNATIONAL RESPONSE"
Ban, who has been visiting camps for Syrian refugees in the region this week, also hit out at the slow international response to the growing refugee crisis, urging donors to increase their assistance with winter fast approaching.
"We have seen a tripling of refugee numbers since July and the numbers keep growing. I am afraid that any signs of escalating violence in Syria will lead to a significant increase in refugee numbers," Ban said.
"Unfortunately, international assistance is simply not keeping up with the needs. I call on all members, especially countries in and around the region, near the region, to ramp up assistance."
More than 465,000 Syrians have already registered as refugees in countries neighboring Syria, the U.N. refugee agency says, and Ban warned last week that figure could surge to more than 700,000 by next month. Tens of thousands of unregistered Syrians have also fled to the region.
Host countries, including Turkey and Jordan, have expressed concern over their ability to cope with the influx of people and have also complained about the slow international response.
While Turkey has built several container "cities" to house the refugees, most of the Syrians in Turkey and other countries are sheltering in tented camps enduring temperatures now hovering around freezing.
At the Zaatari camp in Jordan which Ban visited earlier on Friday, many of the 30,000 refugees complained of inadequate heating and of a shortage of clothing and blankets. Complaints at the often overcrowded camps frequently erupt into protests.
Ban also called on world powers and the U.N. Security Council to unite and take action to end the Syrian conflict, saying a military approach was a "dead-end" and that only a political solution could stop the bloodshed.
He said the international community had not yet started to discuss the possibility of arranging safe passage for Assad and his family out of Syria should he be persuaded to leave.
(Writing by Nick Tattersall and Jonathon Burch; Additional reporting by Suleiman Al-Khalidi in Zaatari, Jordan, and Ece Toksabay in Istanbul; Editing by Pravin Char and Andrew Osborn)