Colombo: Sri Lankan authorities have ordered a state of emergency to be introduced from midnight Monday following the deadly Easter attacks, the president's office said.
The special measures are being brought in "to allow the police and the three forces to ensure public security," the statement said, referring to the army, navy and air force.
The Lankan government believes a local Islamist extremist group called the National Thowheeth Jama'ath (NTJ) was behind the suicide bomb attacks that killed nearly 300 people on Sunday.
Government spokesman Rajitha Senaratne, who is also a cabinet minister, added that the government was investigating whether the group had "international support".
"We don't see that only a small organisation in this country can do all that," he said.
"We are now investigating the international support for them, and their other links, how they produced the suicide bombers here, and how they produced bombs like this."
Documents seen by AFP show Sri Lanka's police chief issued a warning on April 11, saying that a "foreign intelligence agency" had reported NTJ was planning attacks on churches and the Indian high commission.
Not much is known about the NTJ, a radical Muslim group that his been linked to the vandalising of Buddhist statues.
A police source told AFP that all 24 people in custody in connection with the attacks belong to an "extremist" group, but did not specify further.