LONDON, Aug 4 (Reuters) - British prompt wholesale gas prices rose on Thursday morning due to lower wind output but Dutch prices declined amid steady Russian gas flows.

The British day-ahead contract rose by 28 pence to 315 pence per therm by 0843 GMT, while the within-day contract rose by 31 pence to 315 pence per therm.

The UK system was under-supplied by around 5 million cubic metres (mcm), National Grid data showed.

Wind output in the UK has fallen which will increase gas-for-power demand. Peak wind generation is forecast at 4.3 gigawatts (GW) on Thursday and 4.9 GW on Friday, out of total metered capacity of nearly 20 GW, Elexon data showed.

However, UK Continental Shelf flows are higher after a reduction yesterday due to mainentance outages.

An outage at the InterconnectorUK pipeline between Britain and Belgium has been extended, impacting exports to the continent.

In the Dutch market, the front-month gas contract fell by 2.90 euros to 196 euros per megawatt hour (MWh), while the November contract was down 7.30 euros at 199.50 euros/MWh.

Russian flows to north-west Europe are stable but still heavily reduced with the saga around Nord Stream turbine continuing, said Marina Tsygankova, gas analyst at Refinitiv.

German Chancellor Olaf Scholz said Russia had no reason to hold up the return of a gas turbine for the Nord Stream 1 pipeline that had been serviced in Canada but has since been stranded in Germany in an escalating energy standoff.

The second-largest U.S. liquefied natural gas exporter said it reached an agreement with a federal regulator that will allow it to resume some operations at its Quintana, Texas, plant in October, which could also be bearish for prices, traders said.

In the European carbon market, the benchmark contract edged up by 0.71 euro to 84.70 euros a tonne.

(Reporting by Nina Chestney)