LONDON - Oil prices fell on Monday as worries over China's economy resurfaced after a survey showing growth in factory activity slipped sharply in the world's second-largest oil consumer, with concerns compounded by higher crude output from OPEC producers.

Brent crude oil futures slid by 87 cents, or 1.15%, to $74.54 a barrel by 1145 GMT after touching a low of $74.10.

U.S. West Texas Intermediate (WTI) crude futures dropped $1, or 1.4%, to $72.95 after slipping to a session low of $72.77.

"China has been leading economic recovery in Asia and if the pullback deepens, concerns will grow that the global outlook will see a significant decline," said Edward Moya, senior analyst at OANDA.

China's factory activity growth slipped sharply in July as demand contracted for the first time in more than a year, a survey showed on Monday. 

The weaker results in the private survey, mostly covering export-oriented and small manufacturers, broadly aligned with those in an official survey released on Saturday. 

Also weighing on prices, a Reuters survey found that oil output from the Organization of the Petroleum Exporting Countries (OPEC) rose in July to its highest since April 2020. 

The United States will not lock down again to curb COVID-19, but "things are going to get worse" as the Delta variant fuels a surge in cases, mostly among the unvaccinated, President Joe Biden's chief medical adviser Anthony Fauci said on Sunday. 

The United States and Britain on Sunday said they believed that Iran carried out Thursday's attack on an Israeli-managed petroleum products tanker, which killed a Briton and a Romanian, and pledged to work with partners to respond. 

(Additional reporting by Jessica Jaganathan in Singapore Editing by David Goodman ) ((Jessica.Jaganathan@thomsonreuters.com; +65 6870 3822; Reuters Messaging: jessica.jaganathan.thomsonreuters.com@reuters.net; Twitter: https://twitter.com/j3ssi3))