Heavily armed soldiers took up positions around the capital while police stepped up random vehicle searches, a senior police officer told AFP.
"There is a greater military deployment to assist the police with the security arrangements," the officer said on condition of anonymity.
The new measures are part of the government's decision to reimpose a security clampdown that was in force before the February 2002 ceasefire with the rebel Liberation Tigers of Tamil Eelam (LTTE).
They come amid a surge in violence that has killed hundreds in recent months and left the truce in tatters.
The military announced the measures Monday, shortly after Major General Parami Kulatunga, the army's number three commander, was killed by a suspected Tamil Tiger suicide bomber.
Government defence spokesman Keheliya Rambukwella warned Tuesday of even stricter measures but declined to give details. "We will do everything necessary to protect national security," Rambukwella said.
"The measures will be even