UK GAS-Prices rise on concerns about Russian gas supply cut

* System opened undersupplied, then balances out

* Concern about Russian supply to Europe prompts buying

* Analysts cut FY and summer gas price forecasts

LONDON, April 11 (Reuters) - British wholesale natural gas rose on Friday morning as concerns Russia could cut off gas supplies boosted demand from traders.

Gas for next-day delivery moved up by 0.60 pence to 52.20 pence per therm from Thursday's close, while gas for weekend delivery was up 1.25 pence at 51.50 pence per therm.

The British gas system opened undersupplied by around 19 million cubic metres, but by 0814 GMT supply and demand were largely balanced as imports from Norway stabilised.

From Norway, a drop in supplies through the Langeled pipeline early on Friday was offset by higher deliveries through the FLAGS pipeline and a restart of the Vesterled pipeline.

Britain also was exporting gas to the continent on Friday through the InterconnectorUK.

National Grid (LSE: NG.L - news) data showed gas flows at around 208 million cubic metres (mcm) per day and demand at around 209 mcm, about 15 percent below the seasonal norm of 245 mcm.

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Further along the curve, gas prices for June were up 1.43 pence at 51.43 pence per therm, and the third-quarter contract was 0.50 pence higher at 52.85 pence per therm.

Concerns about the situation in Ukraine and the potential disruption of Russian gas supplies to Europe have been driving up prices this week.

On Thursday, Russian President Vladimir Putin warned European leaders that Russia would cut natural gas supplies to Ukraine if it did not pay its bills and added that this could lead to reduced onward deliveries to Europe.

Against this background, a supply disruption sooner rather than later seems very likely, analysts at consultancy Energy Aspects said.

The analysts nevertheless revised their summer 2014 average gas price forecast to 47 pence per therm from 55 pence previously. They also reduced its full-year forecast by 20 percent to 55 pence per therm.

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(Reporting by Nina Chestney; editing by Jane Baird)