FRANKFURT— Siemens AG signed an agreement late Monday to upgrade Iran’s aging railway infrastructure, in the German engineering conglomerate’s latest effort to capitalize on the Islamic Republic’s nascent economic opening.

As part of the deal agreed with Iran’s industrial MAPNA Group, Siemens plans to supply components for 50 diesel-electric trains to be developed locally for the country’s state-owned railway system, the company said.

The deal was signed during an official German delegation visit to Iran that included the economics minister, Sigmar Gabriel, and German business officials.

The agreement comes on the heels of a series of contracts signed last March between Siemens and MAPNA to develop Iran’s energy infrastructure, including a license agreement under which MAPNA would acquire the technological know-how to manufacture Siemens F-Class gas turbines. Siemens also has plans to partner with MAPNA to help modernize Iran’s power and electrification system, the firms have said.