(CNN) -- Public transport in the Belgian capital, Brussels, was paralyzed for a fourth day Tuesday after staff walked out to protest the death of a co-worker in an assault.
Guy Sablon, a spokesman for the company that runs the Brussels public transport network, STIB, told CNN there are no buses, trams or trains operating in the city.
The workers have demanded new security measures to keep staff safe.
The city's transport network was shut down Saturday after a traffic accident involving a car and a bus led to a fatal assault.
Sablon told CNN that a friend of the car driver had punched an STIB supervisor who was taking pictures of the accident scene.
When the man saw the supervisor taking the photographs, "he completely lost it," Sablon said. "He then punched him in the face, and unfortunately this punch killed the supervisor."
Sablon said the attack was not an isolated incident.
"Every day, our staff suffer aggressive abuse from clients, so they have unfortunately gotten used to aggressive situations," Sablon said.
"Therefore, we have endorsed this strike and demanded measures from the government."
Both the Belgian government and the STIB announced new measures Monday evening.
STIB announced that it will recruit 50 new security officers, on top of the 190 officers it already has. As a short-term response, it will also move some of its staff from duties such as checking tickets to security roles.
The government also announced that it would hire 400 new police officers, dedicated to working on the public transport network.
"Now the unions have to explain these measures to their members. We had hoped that they would be back at work this morning, but they were not ready to return to work. So we will see how long the strike will last," Sablon said.
"These are very good measures, and they will have a big impact. It will just take some time to implement them," he added.
Brussels is home to NATO, the European Commission and European Council, as well as many other international organizations.