Brussels public transport workers decided Tuesday to extend their strike by at least two more days, keeping buses, trams and metros idle for almost a week after a colleague was fatally beaten.

The work stoppage, which was on its fourth day, will continue until at least Thursday, the same day as the funeral for a supervisor who died after being punched in the face following an accident between a bus and a car.

The government announced Monday plans to deploy 400 extra police officers in Brussels and recruit 50 agents for the public transport system following Saturday's assault, but it will take months to materialise.

But unions demanded quicker action to stem what they see as an alarming number of attacks on public transport workers.

"We see that no immediate, concrete measures were taken. As usual, there are only proposals and promises," said Adriano Catalano, an official at the CGSP union.

"We voted unanimously against returning to work and this will last as long as necessary," he told reporters.

Around 100 workers protested in front of the headquarters of the public transport administration, STIB, on Tuesday, one day after 1,500 people demonstrated to denounce acts of violence against staff in the network.

Public transport workers have held short strikes in the past when drivers or other staff were attacked in the Belgian capital, which is home to NATO and European Union headquarters.

The STIB decided to close down the network for three days after Saturday's attack, but it asked employees to return to work on Tuesday, urging them to "look beyond emotions and return to reason."

But employees refused to return to work on Tuesday.

The supervisor, 56-year-old Iliaz Tahiraj, was punched in the face by a friend of the driver of the car and died later in hospital.

A suspect, Alexandre Vander Elst, 28, was remanded in custody after giving himself up to police.