A stronger US dollar, as investors shied away from risk on concerns about a slowdown in global growth, also weighed on oil prices, making the commodity more costly for holders of other currencies.
Brent crude had slipped 67 cents to $113.83 a barrel by 0245 GMT, after a 2.4 percent rise on Tuesday to its highest since Sept. 18.
US crude fell 62 cents to $91.77 a barrel. The dollar index rose 0.23 percent.
"There's definitely a little bit of profit-taking after such a strong session," said Ben Le Brun, a market analyst at OptionsXpress in Sydney.
"The rising tension between Turkey and Syria is underpinning oil prices."
The two neighbours have repeatedly exchanged fire since last week after Syrian shells struck a border town in Turkey killing five civilians.
NATO said it has plans in place to defend Turkey against attack from Syria, and will aim to provide assistance if Ankara asks for it.
"The geopolitical risk premium was boosted from mounting tensions between Turkey and Syria," ANZ analysts said in a note.
"This has increased supply disruption concerns, particularly if the Syrian conflict begins to hamper oil production in northern Iraq."
Tensions in the Middle East and delays to North Sea Forties loadings pushed Brent's premium to US crude to its widest in nearly a year at $23.13 a barrel on Tuesday.
Reuters market analyst Wang Tao said the spread may have peaked in a support zone between $22.79 and $24.34 per barrel and could narrow towards $16 over the next four weeks.