At least 25 people were killed and 60 injured on Sunday (April 9) when an explosion rocked a Coptic church in Egypt's Nile Delta, state television reported, the latest assault on a religious minority that has increasingly been targeted by Islamist militants.

Mobile phone video from inside the church obtained by Reuters showed wrecked church pews and shocked congregation standing inside. Blood stains could be seen on the floor and wrecked furniture.

There was no immediate claim of responsibility. The cause of the blast, just one week before Coptic Easter and the same month that Pope Francis is scheduled to visit Egypt, was not known.

The bombing in Tanta, a Nile Delta city less than 100 kilometres outside Cairo, comes as Islamic State's branch in Egypt appears to be stepping up attacks on Christians and threatening them in messages blasted out to followers.