An agreement has been signed opening the way for United States involvement in South Africa's pebble bed nuclear reactor project, the US embassy in Pretoria said on Wednesday.

It said the pact was signed in Vienna on Monday by US Energy Secretary Steven Chu and SA Energy Minister Dipuo Peters.

The pact would boost research and development co-operation in the area of advanced nuclear energy systems. One area of co-operation was expected to be research on the pebble bed reactor. Engineering skills and infrastructure would be another strong area of focus.

"The two countries will collaborate in research and development of advanced technologies for improving the cost, safety, and proliferation-resistance of nuclear power systems," the embassy said.