Schools were cordoned off during operation

They contained explosives but no detonator.

The police are blaming loyalists for leaving the devices.

Huge security operations have ended in both towns.

Staff discovered the bombs on Monday in the playgrounds of the two Catholic schools shortly after 0800 BST.

Kevin O'Neill, the caretaker of St Patrick's College, Dungiven, found the device in his school's car park. "I just opened up the school as normal at 0800BST this morning," he said.

"I saw one device lying in the middle of the car park. It looked suspicious. I immediately phoned the police, they were there within 15 minutes. I just decided to evacuate the place."

Almost 400 pupils were sent home during the Dungiven alert.

Anne Scott, the principal of St Patrick's, said: "I am horrified to come in and find this. It is just dreadful. We can't send our children out to school on a Monday, but they are in danger."

St Patrick's principal Anne Scott was "horrified" by the attack

Ten miles away at St Mary's High School, Limavady, a bomb was found at the front of the school and the area was evacuated.

The principal of St Mary's, Celine McKenna said: "The school is right on the main street.

"We have 900 pupils, the controlled school next door has over 800 pupils making their way along the street early in the morning. We also have primary school children - a lot of traffic - so clearly a lot of lives were put at risk."

During the alert in Limavady, Mass at a nearby church was cancelled.

PSNI Inspector Bob Morrissey said: "This is absolutely disgusting to say the least.

"Targeting children trying to get an education is a real low; putting children's lives at risk. It has to stop now."