Restrictions were also imposed on social media networks and messaging applications including Facebook and WhatsApp, after the attacks in the country. The decision was taken to prevent false information and rumours.
Authorities said some of the attacks done in coordination were suicide bombings.
From 1983 to 2009, Sri Lanka was in a state of civil war. The clashes between the Sri Lankan army and the Tamil Tigers ended with the defeat of the Tamil Tigers, who demanded independence.
More than 70,000 people are believed to have been killed in the civil war, including about 40,000 minority Tamils.
Since the defeat of the Tamil Tigers, no such big attacks were organized.
In the country where most of the population is Buddhist, tension rises between Muslims and Buddhists from time to time.
In Sri Lanka, a curfew was declared in some parts of the country after the attacks of some Buddhists targeting mosques and Muslim businesses last year.