June 9 (Reuters) - British wholesale gas prices plunged on Thursday afternoon due to an expected outage at the Interconnector UK (IUK) gas pipeline connecting Britain with Belgium.

The British gas contract for next day delivery fell by 60.5 pence to 25.50 pence per therm by 1421 GMT, while the contract for within-day delivery fell by 53 pence to 35 p/therm.

The available capacity at the IUK was reduced on Thursday and will be offline on Friday due to filter blockage, operator Fluxys said..

The pipeline will be offline completely from 0400 GMT until 1300 GMT on Friday for a filter change, it said in a separate statement.

Dutch wholesale gas prices cooled off after they rose sharply on Thursday morning, driven predominately by news of an outage at the Freeport liquefied natural gas (LNG) plant in the United States, a key supply point for European customers.

The Dutch gas day-ahead contract jumped by 5.0 euros to 82.75 euros per megawatt hour (MWh), while the July contract rose by 5.6 euros to 84.40 euros/MWh.

Freeport LNG will shut for at least three weeks following an explosion, with the impact estimated at some 1 million tonnes of LNG, traders and analysts said.

"In a context of weak Russian supply, LNG is the main element that has prevented European gas prices from returning to their March highs," analysts at Engie EnergyScan said in a morning report.

The shutdown of Freeport LNG changes that picture, especially if some Asian players decide to return to the market for precautionary purchases, reviving competition with Europe, they added.

"If the impact is purely 1 million tonnes, then the price impact is an overreaction. But people remember Hammerfest, which took a lot longer to come back," a trader said, adding a risk premium was now priced in for a longer outage.

The Norwegian Melkoeya LNG plant in Hammerfest, operated by Equinor, only restarted this month following a near two-year outage after a fire damaged the facility.

Meanwhile, a lingering supply impact from ongoing maintenance in Norway and a dip in Russian gas flows through the Nord Stream 1 pipeline, added to a tighter supply picture, the trader added.

Britain’s gas system was undersupplied by around 1.7 million cubic metres (mcm), National Grid data showed.

In the European carbon market, the benchmark contract rose by 1.9 euros to 81.74 euros a tonne. (Reporting by Nora Buli in Oslo and Marwa Rashad in London; Editing by Susanna Twidale and Alison Williams)