As part of stepped-up security measures, the 39-storey office complex in the heart of Colombo blocked all vehicles from entering, Colombo's police chief Pujith Jayasundara said.
"Following information regarding security, we have taken this measure," Jayasundara said. "Even vehicles of security forces were not allowed into the area today.
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Sri Lanka's stock market, the main offices coordinating the government's peace process with Tamil Tiger rebels, and several ministries are all located within the World Trade Centre (WTC).
A truck packed with explosives targeted the WTC in October 1997, killing 20 people and wounding more than 100.
Another truck bomb that hit the nearby Central Bank in January 1996 left 91 people dead and wounded 1,400.
In both cases authorities blamed the Liberation Tigers of Tamil Eelam (LTTE) who are fighting for a separate Tamil homeland in the country's northeast.
Police barricaded the area surrounding the WTC, preventing office workers in neighbouring buildin