A wave of bombings that killed 290 people in Sri Lanka on Sunday was carried out with the support of an international network, officials said.
The government has blamed a little-known local jihadist group, National Thowheed Jamath, although no-one has yet admitted carrying out the bombings.
Another 500 people were injured in the suicide attacks on churches and hotels.
Police arrested 24 people in a series of raids and the president’s office declared a state of national emergency.
The emergency declaration, which comes into effect from midnight (18:30 GMT) on Monday, will give police and military extensive powers to detain and interrogate suspects without court orders.
Mr Senaratne said that authorities believed the bombers had international support. “We do not believe these attacks were carried out by a group of people who were confined to this country,” he said, adding: “There was an international network without which these attacks could not have succeeded.”
A later statement said President Maithripala Sirisena would ask for foreign help to track down the international links to the attackers.
“The intelligence reports [indicate] that foreign terrorist organisations are behind the local terrorists. Therefore, the president is to seek the assistance of the foreign countries,” his office said.