Protesters gathered outside the hospital where the 20-year-old woman, Semira Adamu, died after police officers travelling with her on a flight to Togo tried to restrain her by putting a pillow over her mouth.

Louis Tobback: application "considered unfounded"

At another demonstration, near the home of Interior Minister Louis Tobback, protesters demanded his resignation.

The Belgian Committee against Expulsions has also called on Mr Tobback to step down.

"We want the immediate resignation of the Interior Minister and the Director of the Bureau for Foreigners," a statement said.

The Belgian Government has ordered an investigation into the incident, which was also filmed by police, as Ms Adamu had earlier strongly resisted four attempts to expel her.

Ms Adamu fled Nigeria last March and applied for asylum because her family was forcing her to marry a 65-year-old man, who already had three other wives.

But a statement from Mr Tobback said her application "... was rejected because it was considered unfounded". The statement added that the procedure for expulsions had been followed and the use of pillows was allowed.

The gendarmes escorting Ms Adamu put the small pillow on her mouth when she started shouting aboard a Sabena passenger flight bound for Togo on Tuesday.

As passengers looked on, Ms Adamu struggled, then fell into a coma. She was taken to hospital where she died hours later of a brain haemorrhage.

Two of the gendarmes taking part in the forced expulsion were charged on Wednesday with "assault unintentionally causing death," Belgian radio reported.

Politicians from the ruling centre-left coalition and the opposition called for a reform of the asylum procedures and many expressed outrage that the use of a pillow to subdue recalcitrant asylum seekers was standard practice.

"The asylum policy has to be humane," Senator Bert Anciaux, chairman of the opposition ID21 party said.

The human rights group Amnesty International has also condemned the asylum laws.

"The death of Semira is part of a series of complaints and is the result of several new laws to get asylum in Belgium," said spokeswoman Joelle Noel.

Some 4,000 people whose asylum requests were turned down by the Belgian authorities were repatriated last year. Some 300 needed police escorts.