Supply trouble at one of the world’s biggest liquefied natural gas exporters signals that disruptions to the market may continue for months.

Edison SpA, the Italian unit of French utility EDF, said QatarEnergy extended a force majeure notice, withholding four additional LNG cargoes scheduled for Italy’s Adriatic LNG terminal until early September.

The latest extension brings the total cargoes affected over the delivery period from April to early September to 21, equivalent to about 2.7 billion cubic meters of natural gas, Edison said in a statement Tuesday.

QatarEnergy issued its first force majeure notice in March, after Iranian missile attacks damaged two LNG-producing trains at Ras Laffan, the world’s largest LNG export facility. That incident curtailed production by 12.8 million tons a year, or about 17% of Qatar’s LNG exports.

Edison said it has replaced 14 of the 21 cargoes with alternative supply and doesn’t expect the shortfall to affect its end customers.

QatarEnergy has estimated the Ras Laffan damage will cost $20 billion a year in lost revenue and take up to five years to repair. The company did not respond to CNBC’s request for comment.

Edison holds a 25-year contract with QatarEnergy, in place since 2009, for the supply of 6.4 billion cubic meters of natural gas annually to Italy.