Thai police said on Monday they were holding a third Iranian for questioning in connection with an alleged plot to kill Israeli diplomats in Bangkok.
The man, who has denied any links to a string of botched blasts in the Thai capital on February 14, was charged with overstaying his visa, said Police Lieutenant General Wiboon Bangthamai.
According to Thai media, mobile telephone call logs showed he had been in regular contact with two Iranians now in custody, one of whom was badly hurt as he hurled a bomb at police while fleeing.
An Iranian couple were also taken in for questioning but were later released because police found nothing to indicate they were involved, Wiboon said.
Another suspect was detained earlier this month in Malaysia, while arrest warrants have been issued for two more Iranians believed to have left the country.
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Israel has blamed Iran over the Bangkok blasts, as well as attacks on Israeli embassy staff in India and Georgia a day earlier.
Tehran has rejected accusations that it is behind a terror campaign against the Jewish state.
Thai police have said they believe that Israeli diplomats were the intended target of the botched plot but have yet to produce hard evidence.
Last week Tehran said it was ready to help identify those responsible.
Bangkok has been on alert since mid-January when police arrested a Lebanese man with alleged links to Hezbollah on suspicion he was planning an attack, following a US warning that tourists might be targeted.
The safety scares dealt a new blow to the kingdom's tourism industry, still recovering from the fallout of months of devastating floods last year, as well as several rounds of political unrest in recent years.