"The three suspects stayed in different hotels in Pattaya," an immigration officer in the coastal city who did not want to be named told AFP.
Police have tracked down a Thai woman known as "Nancy" who escorted one of the men, Mohamad Khazaei, during his stay, he added.
"The most important evidence we found are pictures in Nancy's mobile phone taken on the night of February 11 which prove that these suspects know each other," the officer said.
Pattaya, about a two-hour drive southeast of Bangkok, has earned a reputation for its wild nightlife thanks to its thriving red light district.
According to the Bangkok Post daily, the Thai woman was also in the suspect's hotel room "but didn't detect any irregularities except one time when he barred her from approaching a closet in the room."
The English-language daily published a photograph that it said showed the three suspects relaxing in a hotel bar with two Thai female companions, under the headline: "Suspects partied in Pattaya."
Thai police chief Phrewphan Damapong said Thursday that Israeli diplomats were the intended target of the botched plot, which came to light following an apparently accidental explosion at a house in Bangkok on Tuesday.
One of the men -- named as 28-year-old Saeid Moradi -- had his legs blown off as he hurled a bomb at Thai police while fleeing.
Khazaei was detained trying to board a flight out of the country.
Thailand charged Moradi and Khazaei on Wednesday in connection with the third bomb incident to shake world capitals in less than 24 hours, but Tehran has rejected Israeli accusations that it is behind a terror campaign.
Bangkok is seeking the extradition of a third suspect arrested Wednesday in Malaysia after fleeing the kingdom.