More than 3,000 prison inmates lined up on Thursday to form the Thai symbol for the number nine, in honor of late King Bhumibol Adulyadej, who died on Oct. 13 after reigning for seven decades.



Thailand has entered a year-long mourning period for the king, formally known as King Rama IX and the ninth of the 234-year-old Chakri Dynasty, who was seen as a unifying figure in the politically fractious country.



As many as 3,699 male inmates of the Central Correctional Institution for Young Offenders in Pathum Thani province, 40 km (25 miles) north of the capital, Bangkok, stood in the grounds of the prison complex and sang songs dedicated to the late king.



The men, many of them jailed for drug convictions, were accompanied by a marching band.



The activity, which was compulsory for inmates, is part of many similar events across Thailand amid an outpouring of grief.



"Many inmates wanted to do something to show their loyalty to His Majesty," prison commander Narongsak Sompat told Reuters.



Crown Prince Maha Vajiralongkorn, 64, is the king's designated successor, but junta chief Prayuth Chan-ocha told the country hours after the king's death that the prince had informed him he was not yet ready to assume the throne.



Prayuth said last week the prince could become king in seven to 15 days after the king's death, or later. His coronation, however, cannot take place until after the royal cremation, in a year's time.



The government has moved to quash uncertainty surrounding the succession and to reassure the country that the king's death will not derail plans for a return to democratic rule, which include a general election in late 2017.



It has also gone after critics of the monarchy and enforced tighter censorship of internet comments perceived to be insulting to the royals.