UN Secretary General Ban Ki-moon was due on a one-day visit to Turkey on Friday, where he was to hold talks on war-ravaged Syria and visit refugees displaced by the 21-month conflict.

Ban was to begin his visit with a trip to a refugee camp in the border town of Islahiye, which currently houses some 8,500 Syrians who have fled the violence in their country.

Since the uprising against Syrian President Bashar al-Assad first erupted in March 2011, more than 135,000 Syrians have crossed into Turkey, according to official figures provided by the government. Activists say that actual number is likely to be much higher.

Ban will then head to Ankara, where he will hold talks with President Abdullah Gul and Prime Minister Recep Tayyip Erdogan before leaving the country on Saturday.

Ban's visit comes amid international warnings to the Assad regime not to use chemical weapons to combat the armed revolt in the war-ravaged country.

Speaking in Iraq on Thursday, Ban said Assad should be "brought to justice" if his Damascus regime uses chemical weapons against its own people.

"I have expressed my gravest concerns to (the) government of Syria and I have sent a letter directed to President Assad a couple of days ago," Ban told a news conference in Baghdad.

"I have warned that in any case, if chemical weapons is used, then whoever (it) may be will have to be brought to justice, and it will create serious consequences to those people," the UN secretary general said.

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 uses chemical weapons against his own people.

Ban's visit also comes after NATO gave the go-ahead for deployment of Patriot missiles on Turkey's volatile border with Syria for defence purposes following a series of cross-border shelling -- stoking fears in Ankara over a spillover of Syria's civil war.

In recent weeks, Ban has repeatedly warned against the Syria conflict spilling over into Turkey, a one-time ally of the Damascus regime which is now one of its harshest critics.

The Turkish military has boosted troop numbers along the frontier and has retaliated after Syrian shelling on its soil.