The consortium that built the Mexico City Metro's Line 12, currently out of service to allow for repairs of structural defects, said Wednesday the rails complied with safety standards and blamed the system operator for using the wrong kind of trains.

The rails as originally designed and approved are incompatible with the trains that were subsequently acquired to run on the line, the consortium made up of France's Alstom and Mexican companies ICA and Grupo Carso said in a statement.

"That has caused premature wear and tear along the entire track system, since the wheel design is not compatible with the type of rail specified by the PMDF," the decentralized agency charged with arranging for construction of the new line, the statement added.

The director of the capital's metro system, Joel Ortega, said Tuesday that service had been suspended at 12 stations on Line 12, inaugurated in October 2012, due to rail unevenness, high levels of vibration and wear and tear.

He also said an investigation would determine if any official or construction company involved in the project was legally liable for the structural defects.

Line 12, built at a cost of $1.7 billion, is 25 kilometers (15 miles) long, has 20 stations - eight of them below ground - and provides service in seven Mexico City boroughs.

It transports some 400,000 passengers per day.

Undulatory rail wear, discovered on one 14-kilometer (8.6-mile) stretch of the line, caused damage to wheels and knocked six of the 30 trains out of service, according to a report by an engineering firm.

The unevenness also triggered high levels of vibration, caused a power line to fall and produced cracks in the cars and railway fasteners.

The consortium, however, said in its statement that the rail project was certified by reputable engineering companies.

It added that a separate contract for the delivery of the trains was awarded to Spanish railway vehicle manufacturer CAF 18 months after the construction project began.

That company, for its part, denied that its trains were to blame for the structural problems on Line 12, saying the vehicles met the requirements of Mexico City's SCT transit authority and underwent a rigorous inspection process.

Ortega, meanwhile, said Wednesday it would take at least six months to tally up the cost of repairing Line 12. EFE