The Thai premier made the vow at a time when a second explosion hit the city Tuesday, but no one got injured in the latest attack.
Police Senior Sgt. Maj. Worapong Boonthawee said that someone threw an explosive device from a bridge today and blew up at a ferry pier after falling into the river below. He confirmed that nobody got killed or injured. No person or group has claimed responsibility for either blast.
Prime Minister Prayuth Chan-ocha said "some suspects" were seen in security-camera footage. He described the incident as the worst attack in the country's history.
"(In the past) there have been minor bombs or just noise, but this time they aimed for innocent lives. They want to destroy our economy, our tourism," he said.
Chan-ocha added that Facebook messages apparently warning of an imminent danger to Bangkok before the blast came from an "anti-government group" based in the northeast of the country.
The blast on Monday took place around 7 p.m. local time near the Erawan Shrine, a Hindu religious site popular with Thai Buddhists and Chinese tourists.
Thai authorities are currently searching a man who appeared to walk into the shrine Monday wearing a black backpack, and who was spotted shortly afterward without the backpack. The surveillance footage of the suspect was released by the police today afternoon. The man is wearing a yellow t-shirt and carrying black backpack.