The four men were arrested in a rented house on the eastern outskirts of Bangkok on Tuesday, police said.
"We confiscated fuses, electrical parts and others objects that could be used to make a bomb," Police Lieutenant Colonel Arun Thaengnara told Reuters.
The suspects, in their 20s and 30s, had no identity papers or passports but identified themselves to investigators as Pakistani nationals, police said.
They were detained for further investigation.
Major General Banchorn Chavalsilp, a spokesman for the Thai military, said there were grounds for suspecting the men were terrorists.
Their detention was the result of an exchange of information between police and military units, he said.
Nearly 10,000 athletes and officials from 41 countries are registered for the Games.
Pakistan's ambassador to Thailand, Sher Afgan Khan, told Reuters he could not comment on the case because he had not been given details, but asked:
"If the police say they had no identification papers how do they know they are Pakistani?
"I hope they don't turn out to be Pakistanis," he added.
The Thai military has set up a special task force assigned to cope with terrorist threats during the Games, which open officially on Sunday.
Banchorn said the force was equipped to international standards and had been trained by U.S. anti-terrorism units.
"This special force is under the immediate command of Prime Minister Chuan Leekpai, and I would like to assure the international community that this well-trained squad is ready to cope with any terrorists and ensure the safety of the Games," he said.
Banchorn said the squad would deploy personnel at every sports venue for the Games.
He said 16,000 police had been assigned to provide security and direct traffic during the games.
Police have launched a security crackdown on illegal immigration in the run-up to the tournament, citing fears of terrorist attacks.
In the past week they have detained almost 400 illegal aliens, most of them beggars from neighbouring Cambodia.
Reuters
