Optimism brought about by strong economic indicators, particularly a manufacturing survey in the US, dissipated amid fears of a possible escalation in Syria's civil war following a chemical attack that killed scores of civilians.
The US government contends the regime of Syrian President Bashar Assad is responsible.
"Investors are set to stay cautious with one eye on the Syria development" ahead of this week's G-20 gathering of world leaders in Russia and US employment data, said Gary Yau, an analyst at Credit Agricole CIB.
The so-called US non-farm payroll figures, which will be released on Friday, are a closely watched indicator of the state of the country's economy and can set the tone in the markets for weeks to come.
By midafternoon in Europe, Britain's FTSE 100 was down 0.6% to 6 431.80, while Germany's DAX declined 0.8% to 8 118.61 and France's CAC-40 dropped 1.1% to 3 932.68.
Wall Street was weak on the open, with the Dow shedding 0.1% to 14 824.01 and the S&P 500 flat at 1 640.53.
Japan's Nikkei 225 reversed early losses and rose 0.5% to close at 14 053.87, but benchmarks elsewhere in Asia fell.
South Korea's Kospi declined almost 0.1% to 1 933.03.
Australia's S&P/ASX 200 shed 0.7% to 5 161.60 and Hong Kong's Hang Seng lost 0.3% to 22 326.22.