Approval from the police licensing division came only four days before the planned rally on Sunday, SDP said in a statement.

"Because of this delay, the SDP has no choice but to call off the event," said the statement signed by party assistant secretary general Wong Hong Toy.

However, the party said they will make another attempt to stage a rally at a later date.

The approval came more than five weeks after their application for a permit was filed on July 18. The party had earlier criticised the delay in the approval and a police requirement that they hire their own security guards.

Approval for political rallies is rare in the strictly-governed city-state where the government has been accused of restricting freedom of speech.