Heavy-armed policemen have been sent to foreign embassies in Bangkok since Wednesday when letters threatening terrorist attacks reported, Bangkok Post reported on Friday.
Security beef-up was put in place on Wednesday night for the Pakistani and South Korean embassies in Bangkok which on Monday and Wednesday respectively received letters threatening terrorist attacks, Bangkok Post quoted metropolitan police bureau commissioner Thani Somboonsap as saying.
The letters made by an unknown group named "Yellow-Red OverseasOrganization" threatened to attack the above two embassies and those of six other countries for their governments alliance with the United States in the Iraq war.
The group also threatened attacks on airlines and other major facilities of Australia, Japan, Kuwait, Pakistan, the Philippines,Singapore, South Korea and Thailand between April 20 and 30.
Thani said that police are taking the threat seriously and security guard had also been strengthened at the Korean Air and other airlines.
The Thai Embassy to Sweden in earlier April received a letter threatening attack against Thailand if the Thai troops were not immediately withdraw from Iraq.
Over 400 Thai soldiers left for the southern Iraqi city of Karbala on March 15 to replace the first batch of soldiers that had worked there for half a year.
Domestic call for withdrawal has run high after the Madrid bombings and the Thai Senate on Tuesday launched a motion to debate over the withdrawal issue.
Thai soldiers in Iraq are mostly medical staff, mechanists and engineers. Two of them were killed last December in an attack against foreign troops in Karbala.
The security issue has become a major concern of the Thai government since the country is believed to have more involved with the US anti-terrorism war last year, and at the same time southern Thai provinces were caught in unrest this year.
Thailand was granted with the Non-NATO status last October for arresting Hambali, second headman of Jemaah Islamiyah, in August and sending troops to Iraq in September.