The three "Bangkok bombers" suspected of attempting to carry out an attack in Bangkok are more likely to be assassins than terrorists, a senior Thai security official has said. This potentially corroborates Israel's claims the three men were thwarted in an Iranian assassination plot similar to earlier attacks on Israeli diplomats in India and Georgia.

"The exact target we are still investigating, but we are looking at 'who' the target was rather than a general terrorist attack of 'a big city' or 'crowds of people,' " the official said on Wednesday on condition of anonymity. "If it is an assassination attempt, it could be the armed services, drug lords or diplomats. We have to figure out who they were trying to assassinate."

The official said the nationalities of the suspects had yet to be confirmed. "They have Iranian passports and documents, but we haven't concluded that they are in fact Iranian, which is why we are looking in detail at this case," he said.

A fourth suspect was added to the case late on Wednesday after a court approved warrants for the arrests of four people travelling as Iranian nationals, the Bangkok Post reported. They were the alleged bomber Saeid Moradi, 28, Mohummad Hazaei, 42, Masoud Sedaghat Zadeh, 31, and Rohani Leila, 32, a woman who is said to have arrived in Thailand with the others and rented the house where a cache of explosives was found. Leila's whereabouts are unknown.

One of the suspects was detained by Malaysian police in Kuala Lumpur on Wednesday while trying to board a flight to Tehran, the Nation reported.

Further details about the alleged bomber, Saeid Moradi, who lost both legs in the last Bangkok explosion, emerged. He is said to have flown into Thailand on 8 February from South Korea, and spent five nights in the resort town of Pattaya. He checked into the Top Thai hotel with only a backpack, the Bangkok Post reported, and was later joined by a friend who had a large bag with him. The two men hardly left the room, the Post reported. "Mr Moradi was good-looking and dressed neatly, as if he was a young entrepreneur," one member of staff told reporters. "He was also polite and I can't believe that he would be a bomber."

The DIY explosives found in a Bangkok house after a series of blasts rocked the capital on Tuesday were similar to devices used against Israeli embassy targets in India and Georgia, Israel's ambassador said on Wednesday, a day after Israel's defence minister accused Iran of being behind the thwarted attack.

Iran's foreign ministry spokesman Ramin Mehmanparast called the allegations "baseless" and said Israel was attempting to sabotage its relations with Thailand.

Five people, including the alleged bomber, were injured in three explosions in Bangkok's bustling Ekkamai neighbourhood at about 2pm local time. The first explosion occurred at a house rented by three Iranian nationals who, according to police, fled after homemade explosives accidentally ignited. Two men fled while the third, wounded and disorientated from the blast, attempted to hail a taxi before throwing a grenade at the car and another at police. He missed his target and the grenade detonated in front of him, blowing off one leg and requiring the amputation of the other.

In the house, Thai police found and defused two magnetic bombs that could be attached to vehicles, resembling those used in attacks against Israeli embassy targets, said the Israeli ambassador, Itzhak Shoham.

"They are similar to the ones used in Delhi and in Tbilisi," Shoham told the Associated Press. "From that we can assume that there is the same network of terror."

A bomb squad source quoted in the Bangkok Post said that each bomb could cause serious damage within a 40-metre radius, and that such bombmaking methods had never before been seen in Thailand.