THE RUC reissued flak jackets to its officers on duty last night and the issue of firearms was stepped up in response to the ending of the IRA ceasefire.
The nationalist and loyalist working class areas of Belfast, where paramilitary activity has always centred, were reported to be quiet.
However, there were unconfirmed reports that shots had been fired in the lower Shankill Road area and that armed men had been seen there during the evening.
Loyalist sources yesterday reported that a meeting of the joint Ulster Volunteer Force (UVF) and Ulster Defence Association (UDA) is expected to take place in the coming days.
However, last night there was no sign of any officially sanctioned loyalist response to the IRA bombing. Loyalist leaders have recently expressed concern about the IRA's intentions but stressed that their side was committed to a "no first strike" policy.
Earlier yesterday, shots were fired at building workers in the Shankill area but it is not thought the incident was connected with the unexpected IRA renewal of its campaign.
The sight of officers wearing body armour was the first sign of the return to a state of heightened security in response to the IRA threat.
In a statement last night, the RUC Deputy Chief Constable, Mr Blair Wallace, said steps had been taken "to reintroduce such security measures as we consider prudent".
He added "We have made clear from a very early stage that we would respond to the ceasefire in a responsible and progressive manner.
"These measures were kept under constant review and were designed from day one to be capable of being reintroduced at short notice should that prove necessary.
"Steps have now been taken to reintroduce such security measures as we consider prudent. Where necessary this will involve military support."
There was no sign of a return of British army patrols on the streets of Belfast last night.
The British military presence in Northern Ireland has been greatly reduced in the last year. The official line that there are still more than 12,000 troops in the North is not believed to reflect the reality that many of these troops have actually been transferred to other duties in Britain or abroad.
There were also no reports of checks being reintroduced on Border roads last night. Most of the Border checkpoints are still in place but they are either unmanned or have remained open since before Christmas, 1994.
The RUC has worked virtually without British army support since the ceasefire but it indicated last night that, if necessary, it would call on military support again if it was deemed necessary.
Armoured police patrols were reported to have been stepped up in Belfast last night.
. One of the loyalist fringe parties predicted that if there were a "total breakdown" in the IRA ceasefire then it would be difficult to restrain the loyalist paramilitaries. Mr William Smyth, of the Progressive Unionist Party which speaks for the UVF, said he hoped that nationalists would put pressure on the IRA and Sinn Fein to immediately reactivate the ceasefire.
He appealed to loyalists remain calm, and urged the UDA and Red Hand Commando not to come back with a "kneejerk" reaction to the IRA statement and Canary Wharf bombing. He warned however that if the ceasefire totally broke down then it would be very difficult to hold back the Combined Loyalist Military Command from reacting with similar violence.