A public park in Lahore, Pakistan was hit, killing 73 people and injuring hundreds more.
The attack, carried out by a Taliban splinter group, Jaamat ul-Ahrar, was meant to target Christians.
Many of the victims were women and children.
Lahore's Catholic Archbishop, Archbishop Sebastian Shaw, said: "I visited every bedside and every victim, of whatever faith. It was truly difficult because I saw so many children, [aged] only four or five, both Christians and Muslims, who had been wounded or killed by this terrible attack."
According to media in Lahore, many youngsters were playing on the swings and other children's rides in the park when the bomb went off at about 6.35pm on Sunday.
In a move to crackdown on terrorism, Pakistan questioned over 5,000 people, 200 of whom are still in custody. A "huge cache" of weapons has also been seized by the Pakistani army. Reuters News agency said this crackdown shows a willingness of the government to combat terrorism.
But, Wilson Chowdhry, Chairman of the British Pakistani Christian Association, said earlier today that his organisation had warned the government before the attacks that Christians needed extra protection.
"We wrote to the government and explained to them our concerns - that during this Easter period, Christians would need to be protected not only in churches but also in places where they would congregate. It seems that none of our advice was heeded."
Archbishop Sebastian Shaw is calling on Christians in Pakistan to stay strong.
He said: "To my own faithful I said that they must not give up hope because, even though we were going through a period of grave difficulties, we have to learn to rise up again, just as Christ was able to raise himself again, despite carrying the Cross."
Listen to Wilson Chowdhry speaking to Premier's Hannah Tooley on the News Hour.