Six construction workers were killed in a crane crash accident in Iran's capital Tehran on Tuesday evening, official IRNA news agency reported.The crane had been installed in a construction site in the Chitgar district to the west of Tehran where the workers were busy working, the spokesperson for the firefighting department of Tehran municipality told IRNA.Seyyed Jalal Maleki said that the firefighters working to rescue the other people were injured in the crash accident.The cause of incident is under investigation, the report said.