Four policemen protecting schoolchildren were hurt in a blast bomb attack today as negotiations intensified to try to broker a deal and end the violence in north Belfast.

One officer was knocked to the ground and writhed in agony with wounds to his leg when he caught the full force of the explosion. Two officers were treated in hospital for shrapnel injuries to their legs.

The device went off just feet from where RUC officers shielded the children and their parents on their way to Holy Cross primary school.

The so-called Red Hand Defenders, a cover name for the Protestant paramilitary Ulster Defence Association, said it launched the attack.The policemen were hurt while protecting schoolchildren as negotiations intensified to try to broker a deal and end the violence in north Belfast.

A man was being questioned today in connection with the attack, which represents a dangerous new twist to the violent loyalist opposition to the children being escorted through their area of north Belfast.

It followed another night of serious disturbances in the area with bursts of automatic gunfire, as well as attacks on police lines with petrol, blast and nail bombs.

Representatives on all sides, as well as officials at the Northern Ireland Office, are believed to be involved in urgent attempts to agree a settlement to quell the trouble.

Loyalists are also under growing pressure to call off their protests.

Billy Hutchinson, a member of the Progressive Unionist party at the Stormont assembly, is involved in community efforts to ease tensions. He admitted: "This is not the sort of thuggish behaviour we want. The people responsible should be ashamed of themselves."

On day three of the protests, up to 100 children and their parents - a greater number than yesterday - were escorted to the school.

At first, loyalist protesters, fewer in numbers, turned their backs on the children. There was slow hand-clapping.

But as the pupils approached Glenbryn Parade, youths rushed forward to stone police and the blast bomb was thrown.

Several of the terrified children began to cry - one woman fainted - but they were quickly hurried along a security corridor towards the school. The parents returned later.

Hundreds of riot police and troops were involved in another major security operation, and the blast bomb attack angered police chiefs caught up in a bitter and escalating row which has shocked the country.

One of the officers taken to hospital suffered an ear injury.

An RUC spokesman added: "It was a deliberate attempt to injure police. It was an organised attempt to throw a device at our lines."

A police dog was also injured.

One badly shaken parent, Isabel McGrann, who was escorting her seven-year-old daughter Emma to school, said: "When the bomb went off I was scared to turn round to look behind me. I thought the children and parents that were just behind me were dead."

Ms McGrann added that amid the panic, the group were determined to ensure their daughters' safety.

"We had to grab every child we could to get them through the school gates. The kids come first. They are throwing pipe bombs now, I don't think it could get any lower."

The RUC said that in the 24 hours to 5am today, 41 officers and two soldiers had been injured. About 250 petrol bombs and 15 blast bombs had been thrown and four cars set on fire and burned out.

The Northern Ireland security minister, Jane Kennedy, was today meeting political and community leaders in north Belfast today in an effort to end the protests. Ms Kennedy said the attempted blockade must end immediately.

"I think it is important for those that are involved in the violence to understand that our priority must be those children, the safety of the children and the importance of creating an environment in which those children can go to school unmolested," she said.