SINGAPORE - A teenager was travelling on an MRT train when he claimed to have a bomb in his bag and pretended to detonate it by pressing some imaginary buttons.

After that, he placed the bag under a seat in the train and shouted "Allahu Akbar". The Arabic phrase means "God is great".

His antics were recorded and uploaded onto social media platform Instagram.

The other passengers inside the train heard him but court documents did not disclose how they reacted.

The police received a report about the incident the next day.

The 17-year-old Singaporean pleaded guilty on Thursday (March 24) to offences including harassment, theft and rioting.

He cannot be identified as those below 18 are covered under the Children and Young Persons Act.

The teenager was in the train - heading to Serangoon from Hougang - with friends at around 8pm on Dec 26, 2019.

He was seated with his bag on his lap when he loudly said: "Guys, inside my bag (is) the... bomb... So, we're going to bomb the whole station, and everybody inside the train (is) going to die."

After that, he put the sling bag under the train seat, covered his ears and shouted "Allahu Akbar".

In an unrelated incident, one of his friends hatched a plan to steal a gold chain from a Hougang pawnshop and he agreed to take part in the crime.

On Jan 16, 2020, he went to the pawnshop and asked to see its biggest gold chain. He was handed an item that was priced at $7,455 before he ran off with it and went to a nearby pavilion.

He left the gold chain there before the friend, who was in the vicinity, picked it up about 15 minutes later.

The next day, the chain was sold at another pawnshop for about $6,500. The friend later handed the teenager $150.

Separately, the teenager and several other people ganged up to assault their victim in Hougang in the wee hours of May 2 last year.

After the attack, the victim went to Tan Tock Seng Hospital where he was found with injuries including facial wounds.

On Thursday, the court called for a report to assess the offender's suitability for probation.

He is expected to be sentenced on May 23.

It was not disclosed if the friend linked to the theft case and the other members of the group involved in the brawl were dealt with in court.

For harassment, an offender can be fined up to $5,000.

For rioting, an offender can be jailed for up to seven years and caned.

Offenders convicted of theft can be jailed for up to seven years and fined.