The moves follow the detention of a Lebanese man suspected of planning an attack after warnings from the United States and Israel on Friday.
The statements have irked Thailand, which is concerned about damage to its thriving tourism industry and has so far appeared to play down the warnings.
Police detained a Lebanese man reportedly carrying a Swedish passport. Officials said he had links with Hezbollah, a Shi'ite Islamist group in Lebanon backed by Syria and Iran that is on the US blacklist of foreign terrorist organisations.
Thai national police chief Priewpan Damapong told reporters the suspect had maintained that his group had not planned an attack in Thailand but intended to transport the substances to a third country, which he would not name.
Asked about the discovery, Prime Minister Yingluck Shinawatra told reporters: "I have been informed. I would like to ask people not to panic. We are currently in control of the situation."
Thai officials have seemed irritated by travel advisories issued by the US and Israeli governments, followed by several more since Friday. Foreign Minister Surapong Towijakchaikul said diplomats from countries that had issued warnings would meet him for an explanation.
Tourism is a big money-earner for Thailand and ministers are keen not to deter travellers, especially after the hit to tourism from severe flooding in 2011 and political unrest in 2010.
Defence minister Yuthasak Sasiprapha told reporters in the northern city of Chiang Mai on Sunday that Thailand was not the target, although officials have also said that areas of Bangkok frequented by Westerners and Israelis could be hit.
Yuthasak said that a second suspect had managed to leave the country.