The U.K.'s Theddlethorpe gas terminal is offline, a spokeswoman for operator ConocoPhillips (COP) said Tuesday.

Data on the Web site of U.K. gas network operator National Grid shows gas flows from the terminal sank from a rate of around 17 million cubic meters a day just before 0600 GMT Tuesday to zero.

It isn't yet clear why the terminal is offline, and the company declined to say what was responsible for the outage or when normal output was expected to resume.

Traders of natural gas based in London said the outage was due to maintenance and the facility was expected to return to normal operation Sept. 20.

They added the drop in flow had lifted prompt prices, and pegged within day at 21.75 pence a therm and day-ahead at 22 pence a therm.

Company Web site: http://www.conocophillips.com

-By Angela Henshall, Dow Jones Newswires; +44 (0)20 7842 9285; angela.henshall@dowjones.com