Finnish nuclear safety agency STUK said Wednesday it was probing whether safety procedures were respected at the site of a new reactor being built in Finland.

The news came after Greenpeace had called for an immediate halt to construction based on confidential documents it had obtained which said that there were no qualified personnel supervising the welding and that the quality of the welding had not been verified.

STUK insisted the construction site was safe, and stressed its investigation concerned whether the proper procedures had been followed in the supervision of welding work.

"We are looking into the situation with welding directives and welding work, and whether the directives were approved before the work started. In addition we need to look into the qualifications of welding coordinators," STUK assistant director Petteri Tiippana told AFP.

A consortium led by French group Areva is building the world's first next generation pressurised water reactor at the Olkiluoto plant, which will be Finland's fifth nuclear reactor for Teollisuuden Voima (TVO).

Areva's main subcontractor is French building firm Bouygues Construction.

Welding problems were discovered a year ago at the site but had been rectified, STUK said.

"Last year we noticed that there were problems with non load-bearing welds. It was fixed and after that problems have not arisen. If there had been problems, they would have shown up," Tiippana said.

An Areva spokesman said that Bouygues "took the necessary measures to meet the demands of the Finnish safety authorities" a year ago, and said "the quality of the physical work and the quality of the products were not in question."

Tiippana noted that STUK was responsible for checking the welding work of load-bearing joints, not non load-bearing welds, which is supervised by TVO and Areva.

"We have supervised the load-bearing joint work. Safety directives were approved before the work was started, welding was done by qualified workers and the welds have been checked," Tiippana said.

Tiippana said STUK was writing a report for the Finnish Ministry of Economy and Employment on Bouygues' work at Olkiluoto and how the quality of work was checked and by whom. The report is expected to be published next week.

The building of the third nuclear reactor at the Olkiluoto site has run into major delays and is not now expected to start producing electricity until 2011.

Some 25 percent of electricity consumed in Finland is produced in nuclear power plants.