SINGAPORE - Local running group Seletar Hash House Harriers on Wednesday (April 19) apologised for causing alarm and inconvenience in Tuesday's (April 18) security scare at Woodleigh MRT station.

The group explained in a press release that three of its members were marking a trail for its Tuesday evening run that planned to take runners from Bidadari towards Woodleigh Close.

The trio had chosen to use the station's underpass, leaving flour at three to four points within the station's premises, as "this provided the safest route to cross Upper Serangoon Road," it said.

One of its members, a 69-year-old man, was later arrested for causing public alarm, while the two others, aged 53 and 70, are helping the police with investigations.

The man's actions had led to a three-hour closure of the station on Tuesday (April 18), after SBS Transit staff found the white substance suspicious and alerted the police.

The Singapore Civil Defence Force's hazardous materials team was also deployed, while the public was advised to avoid the area.

"In retrospect, they should not have placed any markings in the station, and should have used directional signs instead outside of the station," said the group, which started in 1980 and now has about 100 members.

It added that the three members "stepped forward immediately to identify themselves and have cooperated fully with the authorities", after learning of investigations at the station.

"They are sorry that their actions caused public alarm and inconvenience," the group said, adding that the incident has emphasised to the group the seriousness of the security threat in Singapore.

It also urged members to be more mindful when planning future hash runs, which involve setting trails with flour, chalk or tissue paper, depending on the area.

Hash runners use flour and chalk as it is organic, non-pollutive and can be washed away easily, and in instances where paper is used, such as in nature reserves, runners have to clear it within 24 hours.

There are currently about nine registered hash running groups in Singapore.