BANGKOK, Aug. 18 -- Thailand's Ministry of Foreign Affairs said Tuesday that it is too early to determine the possible motives or perpetrators of a Bangkok explosion that has left at least 20 killed, including four Chinese nationals.

The Thai government expresses its deep condolences to the victims and families of this tragedy, in which an improvised explosive device went off at the Rachaprasong intersection in central Bangkok at about 7 p.m. local time on Monday, the ministry said in a statement.

The perpetrators will be brought to justice, it said, branding the attack, which injured 125 others, including more than 20 Chinese nationals, as a "despicable act."

Prime Minister Prayut Chan-o-cha has expressed deep concern for the victims and instructed security officials to investigate with a view to maintaining public safety and security, the ministry said.

Emergency services and first aid responders were on the scene and those injured have been given full medical attention, according to the statement.

The injured are being treated in nearby hospitals, including Police, Chulalongkorn, Rachavidhi and Ramadibodhi Hospitals.

The Erawan Emergency Service Centre will provide regular updates the conditions of those hospitalized, the ministry said.

The public is also urged to remain calm and monitor the situation regularly while security agencies conduct their operation, it added.