Civil engineering work at the facility, which is being built in Flamanville, is now 20 months behind schedule, sources within Electricite de France said.

They added that the delay for conclusion of the entire project was likely to be about a year.

EDF in 2007 said construction of the reactor would take 54 months, with the completion date estimated for June 2012.

EDF chief executive Pierre Gadonneix said Thursday the facility would enter commercial service in 2013. EDF has until now spoken only of 2012, without drawing a distinction between the start of operations and their commercialisation.

Negotiations on the contract between EDF and Bouygues were not expected to affect the cost of the project, estimated to be 4.0 billion euros (5.9 billion dollars), according to the sources.

There was no immediate comment on the reported talks from either EDF or Bouygues.