Thailand’s prime minister has vowed to introduce new gun control laws in the wake of a shooting by a teenager on the outskirts of Bangkok that left eight people dead and 22 injured.

The 14-year-old killed his grandparents at the home they shared, before travelling to Debsirin School in Nonthaburi, where he was a student. There, he killed five teachers before taking his own life. Later, Thai media reported that a student had also died from their injuries.

Speaking after the attack, Prime Minister Anutin Charnvirakul said he plans to introduce laws that restrict the carrying of firearms in public, with the new legislation only allowing government officials on duty to carry guns.

Police Colonel Thadsakorn Konthong said that the gun and bullets used in the attack belonged to the teen’s grandfather, with an initial inspection finding signs that the firearm had been searched for inside the grandfather’s bedroom.

International and local media have reported that the gun was legally registered and had a permit.

Thailand has one of the highest rates of civilian gun ownership in South East Asia, with around 10.3 million firearms in civilian possession, around four million of which are believed to be owned illegally.

The country has strict gun laws, which punish the illegal possession of arms with up to 10 years in jail, but enforcement of these laws has been an issue.

During his time as interior minister, Anutin introduced a number of gun control laws, including a short-term ban on new gun licenses and import restrictions.

Speaking on Friday, the prime minister said the tragedy “shouldn’t have happened”.

“I don’t just feel sorry for the victims but I feel sorry that this happened. How can this happen in our country,” Anutin added.

The teenager is believed to have shot his 73-year-old grandfather and 74-year-old grandmother at their two-storey flat at around 05:00 local time on Friday (22:00 GMT on Thursday).

Each was killed by a single shot to the head, a Thai police official said.

After killing his grandparents, the teenager boarded a school bus carrying the firearm and dozens of bullets, Reuters news agency reported.

He then attended his first class at 08:30 and his second at 09:20.

Around half an hour into his second class of the day, he drew the gun and began shooting.

The teenager is believed to have first shot teachers on the school’s sixth floor, killing three of them.

“He then walked down the stairs and encountered the school’s deputy director and the director’s secretary, who were going up the stairs to check on the situation,” Police Major General Dejrapee Kongdee told Reuters.

“The attacker shot and killed both of them on the staircase.”

Police were deployed to the scene while the shooting was ongoing. They found the attacker, who by then had shot himself, around 10:40, Dejrapee said.

Five people were immediately killed and at least 23 were wounded. Later, Thailand’s public broadcaster and the Bangkok Post reported that an eighth victim had died.

National police chief Gen Kittiratt Phanphet told reporters that forensic officers had found the attacker’s shots were quite accurate, with several hitting vital spots on the body.

The prime minister said the attack was “well prepared” with “clear steps and clear goals”.

According to local media, police have searched devices belonging to the teenager and found several videos relating to school shootings in the US.

The teenager has been described as quiet and well behaved by family members in local media.

His uncle told Thai media the teen spent much of his time indoors playing violent video games and rarely went outside. He added there was no indication the teenager was planning the attack.

The attacker had lived with his grandparents, as his parents were divorced.

The Debsirin School, founded in Bangkok in 1885, is one of Thailand’s top secondary schools with branches across the country. It counts many prominent Thai figures among its alumni, from diplomats and athletes to several prime ministers.