Stricter security measures will be imposed throughout the capital, and 12 more road checkpoints jointly manned by military personnel will be set up around Chitralada Palace, while seldom-used public phone booths will be removed.

The explosion last Saturday night in Dusit district injured one person and damaged the booth. Police have not discovered who was responsible for the bombing - the 11th since the September 19 military coup.

All 88 metropolitan police stations have heightened security measures at more than 3,000 locations across the capital and set up 84 traffic checkpoints in the wake of intelligence tip-offs warning of anti-government mob protests and planned bomb attacks.

Assistant national police chief Lt-General Jongrak Juthanont dismissed as irrelevant Deputy Foreign Minister Sawanit Kongsiri's interview with foreign media in which he claimed the latest bomb attack was ordered by stakeholders in the party-dissolution cases before the Constitution Tribunal, which is due to deliver its rulings on May 30.

Police have interviewed seven witnesses but made little progress, he said. The time bomb had no shrapnel and was placed by the booth long before it went off at 9.50pm, he said.

Deputy Democrat Party leader Jurin Laksanavisit said his party had nothing to do with the bomb attack and that he had no idea about what Sawanit meant about the five political parties facing possible extinction.

"His statement has somewhat affected all five parties," he added.

Governor Apirak Kosayodhin said a total of 1,370 surveillance cameras would be installed at important spots, including 120 intersections around Sanam Luang and the Royal Palace. The Bt190-million project will begin immediately and take two months to complete.

A survey is underway to determine which of all of the 26,000 phone booths in Bangkok should be removed. A total of 8,671 booths are set to be removed at the request of the Bangkok Metropolitan Administration, and 405 more have already been taken away.