Four workers killed building Tehran metro station

A tunnel collapse killed four workers building a new station on Tehran's metro network, Iran's state broadcaster reported on Thursday.

Another 11 workers were injured, some of them Afghan refugees, when the concrete cladding on the tunnel fell on the construction crew on Wednesday evening, the broadcaster said.

Deputy mayor for traffic and transport Maziar Hosseini said the accident was the result of "human error".

Iran began building its metro system in 1977.

The Islamic revolution of 1979 and the Iran-Iraq war of 1980-88 caused a decade-long delay before construction resumed in the 1990s.

Tehran now has around 100 metro stations and work is ongoing on its sixth line.