The Passenger Rail Agency of South Africa (PRASA) has rejected the DA's call for the auditor general to investigate a R3.5-billion locomotive deal, and said it was outsourced because Transnet would not have been able to deliver.

"We question the Democratic Alliance's economic policy. They are supporting protectionism and inefficiency," PRASA group CEO Lucky Montana said in a statement on Monday.

"They have been big in supporting the private sector, but today they are standing up for Transnet."

The DA was trying to "fool" the country into believing that Transnet would have been able to deliver the locomotives needed to revitalise the rail industry.

The DA said on Sunday that Auditor General Terence Nombembe should investigate the R3.5-billion locomotive deal.

Montana said Transnet had an important role to play in revitalising the industry and was fully supported by Prasa.

However, none of the industry players could meet Prasa's requirements for new locomotives.

Transnet Rail Engineering had been struggling to meet targets in terms of the refurbishment of the existing fleet, Montana said.

DA spokesman Ian Ollis said in a statement Swifambo Rail Leasing was awarded a contract to provide 88 dual, diesel-electric locomotives to Prasa for the Shosholoza Meyl long-distance services, according to media reports last year.

"Swifambo Rail Leasing will be acquiring these locomotives from Vossloh, a Spanish company, at R50-million per locomotive. Local train supplier Transnet Engineering's going rate for locomotives is R25m," Ollis said.

"PRASA's acquisition of locomotives from Vossloh, a foreign company, through Swifambo, is a violation of the Preferential Procurement Policy Framework and Treasury regulations on rail rolling stock, which dictates that at least 55 percent of diesel locomotives and 60% of electric locomotives need to be produced locally," he said.

However, Montana said the DA statement had no merit, and was false because Swifambo Rail Leasing was awarded the contract after an "open and competitive" procurement process where six companies submitted bids.

"It is important to note that Transnet Rail Engineering, for this tender, partnered with GE South Africa Technology," he said.

"Transnet is also buying locomotives from China South Rail and General Electric. They are not manufacturing those locomotives themselves. Why is that the case? The Democratic Alliance has, conveniently, left these facts out of their statement."

It was clear that the DA had "succumbed to a lobby clique within Transnet and elements within the unions" to put pressure on PRASA to use Transnet to provide locomotives, Montana said.

Ollis said South Africa needed to be assured that no tender irregularities had occurred in awarding the contract to Swifambo, and that the R123bn rail rolling stock fleet renewal programme still to come would not also be fraught with irregularities.

"A full investigation is the surest way to achieve this," said Ollis.