Bangkok Mass Transit System (BTS), the operator of the Skytrain, yesterday apologised to a foreign passenger who claimed he was attacked by a security guard for breaching a rule banning gas-filled balloons on the rail system.

The apology followed the filing of police complaints by both sides in the March 16 altercation at Prompong Station.

"We have already removed the guard[s] who were involved from the BTS system," BTS executive Anat Arbhabhirama said yesterday.

He added that negligent officials - who he said were the source of the passenger's dissatisfaction - would also face a disciplinary probe and harsh disciplinary action.