Islamist extremists in Sri Lanka are believed to be planning attacks on bridges in Colombo, the Sri Lankan Police authorities said.
The doubt is strengthened by the fact that several conspirators which killed 257 people in Sri Lankan attack were still at large. Police confirmed they had instructed stations around Colombo to deploy additional officers.
Government also took help of navy to deploy more vessels on rivers, following leaks of police intelligence reports warning that bridges into the capital were at risk of attack.
Sri Lanka's military has also set up a special command centre to coordinate anti-Islamist operations, while the army said more troops have been deployed for search operations.
Additional troops conducted searches overnight and seized explosives and weapons from several locations, although these were from criminal groups and not extremists, official sources said.
The authorities had information about a small group of radicals who may be trying to stage more strikes, said Health Minister and government spokesman Rajitha Senaratne, who added that the crackdown on extremists after the Easter bombings had been largely successful.
But the government was also still on the hunt for "four terrorists" involved in the Easter attacks who were still at large, Mr Senaratne told AFP in an interview on Thursday evening.
The Catholic Church announced on Thursday that it had called off the resumption of Sunday services following information of a "specific threat" against two of their locations just outside the capital.
Catholic schools, which were due to reopen after an extended Easter holiday, will now be shut indefinitely.
Public schools are due to reopen on Monday under tight security.