The Middle East produces about a third of the world's oil
Oil prices have risen to a six-month high amid growing expectations of a military strike against Syria.
The price of Brent crude oil rose above $113 a barrel in London trading, while the price of US crude rose sharply.
Stock markets across Europe and in the US were also down.
Syria is not a significant oil producer, but there are fears for the stability of the wider Middle East region, which produces about a third of the world's oil.
In London, the FTSE 100 index was down by more than 0.6% by 15:00 BST.
Germany's Dax and the French Cac 40 index were both down about 2%.
On Wall Street, the Dow Jones Industrial Average fell more than 0.6% at the open.
Supply woesThe Middle East contains some of the world's biggest oil producers, along with some important shipping routes.
Even before the latest developments in Syria, analysts were forecasting higher oil prices, partly because of supply disruptions.
Libya, one of the Arab world's biggest oil producers, has seen its production drop by nearly 60%, hit by strikes and security concerns.
Goldman Sachs raised its short-term forecast for the oil price to $115 a barrel.
US President Barack Obama is due to outline future US action on Syria in the coming days.
The US, UK and other countries hold the regime of Syrian President Bashar al-Assad responsible for a large-scale chemical weapons attack in outlying areas of Damascus last week.
Source: BBC News - Business http://www.bbc.co.uk/news/business-23848721#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa
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