The occupants of a white Mercedes which sparked a security scare in Rotterdam on Thursday night were trying to find a coffee shop to buy soft drugs, a lawyer representing the three men said on Friday.

One of the three – a 22-year-old Belgian – had been picked up earlier this week in Breda after he was found to be carrying a small quantity of drugs and a gas pistol. The trip to Rotterdam was also to buy drugs, the lawyer said.

Police searched the car, which has Belgian number plates, and found a very small quantity of cannabis, news agency ANP says. The car is reportedly on a watch list of suspicious vehicles and the three Belgian nationals, aged 20, 22 and 23, remain in police custody.

Elsewhere in the Netherlands, there were at least four false alarms.

The immigration service offices in Zwolle were evacuated for a time and explosives experts brought in to deal with a suspect package. ‘It was a package of paper placed in an unusual place in the building,’ a police spokesman told news agency ANP.

Another suspicious packet found in Huizen police station led to the building being evacuated and traffic diverted while it was investigated. That too was a false alarm.

And in Haarlem sniffer dogs were brought in after a ‘suspicious object’ was found in a train. The ‘object’ was not explosives but has been taken away for further research, ANP says.

A street in Amsterdam was also closed for a time after passersby reported a ‘ticking’ waste bin. The noise was caused by a toy.