European stocks dropped to the lowest level in six weeks as concern grew that the U.S. will take military action against Syria.

The Stoxx Europe 600 Index lost 0.4 percent to 297.88 at 4:30 p.m. in London, its lowest level since July 17. The gauge fell as much as 1.1 percent in intraday trading. It has still advanced 8.1 percent since this year’s low on June 24 as the European Central Bank pledged to keep interest rates low. The Stoxx 600 slid 1.8 percent yesterday after U.S. Secretary of State John Kerry said the U.S. will hold Syria accountable for using chemical weapons against its own people. The attack near Damascus last week killed as many as 1,300 people, according to opposition groups.

In the U.K., Bank of England Governor Mark Carney said the central bank is prepared to boost stimulus if the U.K.’s economic recovery is hampered by investors’ expectations of high interest rates.

National benchmark indexes retreated in 11 of the 18 western European markets today.

FTSE 100 6,430.06 -10.91 -0.17% CAC 40 3,960.46 -8.27 -0.21% DAX 8,157.9 -84.66 -1.03%

Accor (AC) dropped 4.2 percent to 27.58 euros, the biggest loss since June 2012. Europe’s largest hotel operator posted first-half earnings before interest and taxes of 198 million euros ($265 million), missing the average analyst projection of 212 million euros. The company predicted 2013 Ebit of between 510 million euros and 530 million euros, compared with the average 534 million-euro analyst estimate.

A gauge of European travel companies slumped to a two-month low, for one of the worst performances among the 19 groups in the Stoxx 600. Air France-KLM slid 2.8 percent to 5.75 euros and Lufthansa fell 3.1 percent to 13.50 euros.

Polymetal International Plc (POLY) lost 5.7 percent to 699 pence as the Russian gold and silver miner posted a first-half net loss of $255 million, compared with a $157 million profit a year earlier.

Bouygues rallied 11 percent to 25.41 euros, the biggest gain since February. The French building, telecommunications and television company’s operating profit increased to 432 million euros from 394 million euros a year earlier. Analysts had forecast 358 million euros, according to the average of three estimates. Separately, Bouygues cut its sales target for the full year to 33.2 billion euros to 33.4 billion euros. That compared with a previous forecast of 33.45 billion euros.

Statoil ASA (STL) rose 4.2 percent to 137.60 kroner. Norway’s biggest energy company made its third oil discovery off the coast of Canada in the Flemish Pass basin. Bank of America Corp. raised the stock to buy from neutral.

Vestas Wind Systems A/S advanced 5.5 percent to 104.90 kroner as Stoxx Ltd. said the company is among the 12 stocks that will be added to the Stoxx 600 as of Sept. 23.