UPDATE 1-Three workers killed in Medgaz accident

(recasts with official source, adds details)

MADRID, Sept 17 (Reuters) - Three workers have been killed, four badly injured and one other is missing after an accident during the construction of an undersea gas platform between Spain and Algeria, the Medgaz consortium said on Wednesday.

The accident occurred in international waters after a crane on the Saipem 7000 platform suffered a mechanical failure, Medgaz said in a statement.

All but one of the workers affected were employed by the Italian oil services group Saipem (SPMI.MI).

The Medgaz project is a deepwater gas pipeline running from Beni Saf, on the Algerian coast, to southern Spain, and is scheduled to be completed by 2009. Medgaz is a consortium of Algerian state company Sonatrach, Spanish groups Cepsa (CEP.MC), Iberdrola (IBE.MC) and Endesa (ELE.MC) and France's GDF Suez (GSZ.PA). (Reporting by Paul Day)