Thaksin, however, refused to give details about intelligence reports which he said pointed to the planned strike.
"Intelligence gathering clearly showed that they were planning to do something which I do not want to elaborate on," Thaksin said in a weekly radio address on Saturday.
The US had announced on Thursday that Hambali, the alleged Indonesian architect of last October's Bali bombings in Indonesia, had been captured in Thiland, along with three other suspects, and was in its custody.
Thaksin said Hambali was being interrogated by allied countries in a secret location but he declined to confirm reports that Hambali had planned to attack the Asia Pacific Economic Cooperation (APEC) summit to be held in Bangkok in October.
The summit will bring together 21 leaders including US President George Bush.
"Originally, I didn't want to speak in any detail because the interrogation is still going on and I want the results of the interrogation to lead to more arrests," Thaksin said.
A Malaysian newspaper reported on Saturday that Zubair Mohamad, one of the Jemaah Islamiyah suspects arrested in Thailand, provided information which led to Hambali's arrest.
Hambali is suspected of orchestrating the 12 October Bali nightclub blasts that killed 202 people, the Marriott Hotel bombing in Jakarta on 5 August in which 12 people died. He is also suspected of links to the 11 September attackers.
Meanwhile, Indonesian officials demanded that Hambali be put on trial in his home country under "anti-terror" laws.
"Based on the law, we can claim jurisdiction on Hambali," Justice Minister Yusril Ihza Mahendra told a news conference.
Indonesian Foreign Minister Hassan Wirajuda said he did not expect Washington to object to allowing Indonesia access to Hambali, though the two countries did not have any extradition treaty.
In other developments Indonesian police said on Saturday they had arrested a number of people in connection with the bombing of the Marriott hotel.
"Yes, we have made arrests," national police chief General Da'i Bachtiar told reporters, but he declined to say when the arrests took place or how many people had been detained.