Police and soldiers maintained a high profile around Catholic schools in north Belfast, to reassure pupils and teachers and to deter loyalists who have threatened to attack the premises.
The day was kept virtually free of trouble, but tensions remained high after a menacing loyalist declaration that Catholic teachers could be "legitimate targets".
Worries are centred on the south-east Antrim section of the paramilitary Ulster Defence Association, which is held responsible for killing Catholic postman aged 20 on Saturday. While some sections of the UDA are relatively quiet, elements in and around north Belfast and other districts have been involved in violence, including killings.
A series of emergency meetings of political leaders, teaching unions and other educationalists were held yesterday, which issued calls for the threat to be withdrawn.
The funeral of the murdered postman, Daniel McColgan, is to be held today. Up to 2,000 postal workers are to stage a 24-hour stoppage in the greater Belfast area. John Keggie, the deputy general secretary of the Communication Workers' Union, said: "We will consider further options if the threat is not removed ... We are not having our members indiscriminately murdered."
The Irish Congress of Trade Unions called for a much wider work stoppage, lasting from noon until midnight on Friday to follow a lunchtime rally at Belfast's city hall. The deputy general secretary, Peter Bunting, said: "We are saying quite clearly to everyone in society this madness must stop."
The high-profile security measures in north Belfast included helicopter flights over schools believed to be at risk. At the Holy Cross primary school at the Ardoyne flashpoint, a dozen police Land Rovers could be seen in nearby streets. Elsewhere police vehicles were parked for much of the day at school gates.
The only incident of note came at a Protestant school that was evacuated after a telephoned bomb warning that turned out to be a hoax. But there were two overnight arson attacks on Catholic schools in south Belfast and in Lisburn, Co Antrim.
The Secretary of State for Northern Ireland, John Reid, denied an accusation from the Sinn Fein president, Gerry Adams, that the government was failing to face up to the threat posed by loyalists.
Last night, police released without charge two people who had been arrested on the day of Mr McColgan's murder. A police spokeswoman said another two people were arrested yesterday.
* A man aged 27 was charged last night with possession of explosives, firearms and ammunition with intent to endanger life. The charges relate to the discovery of arms at a house in Carlisle Road, north Belfast, on Saturday night. A senior police officer linked the discovery, which included primed pipe bombs, an anti-personnel mine, detonators, a sub machinegun, a shotgun and ammunition, to the republican Irish National Liberation Army. The man is expected to appear at Belfast Magistrates' Court today.
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