BANGKOK - Thai Prime Minister Prayut Chan-o-cha has ordered an extensive investigation into the pipe bomb that was recovered in an overgrown lot near a MRT station in Bangkok.

Col Piyapong Klinphan, spokesman of the National Council for Peace and Order, said on Wednesday morning (May 31) that Mr Prayut wanted authorities to find out whether there is a link between the pipe bomb retrieved near the Thailand Cultural Centre subway station on Tuesday afternoon and three recent bomb incidents in the city.

Mr Prayut also ordered authorities to step up intelligence operations and find the suspects behind the incidents.

Mr Piyapong said that police are still investigating whether the pipe bomb's components are similar to the three pipe bombs used in recent incidents.

A pipe bomb exploded in front of the Government Lottery Office on April 5 and another one in front of the National Theatre on May 15. The two were minor explosions that did not cause much damage.

The third pipe bomb explosion was at the Phramongkutklao Hospital on May 22 that injured 25 people.

Mr Piyapong, however, said it was his personal opinion that the abandoned pipe bomb was unlikely to be linked to the three previous bombings. He said it was likely that the pipe bomb was discarded by its owner for fear of arrest amid tightened security in the city.

Police are now looking for two men who were spotted at the site near the subway station where the suspected pipe bomb was found. The steel pipe, about 20cm long and 10cm in diameter, was inside a black plastic bag and placed in a green plastic basket.

Nails appeared to be covered in rust were also found wrapped in plastic inside the basket.

Police said the pipe bomb was live and had to be defused before being sent for forensic examination.

National Police Commissioner Pol General Chakthip Chaijinda earlier said the object was similar to the one at Bangkok's Ratchaprasong intersection in 2015.