AFP - Northern Ireland was on edge Monday after a huge car bomb only just failed to cause devastation at the weekend, in a new threat to the long-troubled province's fragile peace process.

Dissident republicans may even be planning a Christmas "spectacular", reports suggested after two incidents within hours fuelled fears of renewed violence, more than a decade after a landmark peace accord.

The Northern Ireland Assembly, in which once sworn enemies share power in Belfast, was due to meet and was expected to condemn the weekend attacks, which also saw police exchange gunfire with paramilitaries.

"We need to close them down," said Gerry Kelly, a member of the assembly for Sinn Fein, once the political wing of the Irish Republican Army (IRA).

"People don't want a return to the place where these people want to bring us back to .. We need to show them that the community is moving on and we are moving on with politics," he told BBC radio.

In the most alarming attack of recent months, a car containing a 400-pound (180-kilogram) device crashed through barriers outside a police headquarters in Belfast late on Saturday and partially exploded, police said.

A police spokeswoman said two men were seen running away from the car after it crashed through the barriers of the province's policing supervision board.

Half an hour later, a small explosion went off inside the vehicle. "Had this device functioned as the terrorists planned, there would certainly have been widespread damage and destruction," the spokeswoman said.

"It is also very probable that this 'no warning' device would have led to very serious injury or loss of life," she added.

Northern Ireland police chief Matt Baggott called it "a reckless act -- not just in doing damage but also the potential loss of life."

Almost at the same time, police exchanged shots with paramilitaries in a border village. Three people had been arrested in Northern Ireland and one across the border in the Republic of Ireland, police said.

According to the Times newspaper, security forces fear that the dissidents will succeed in mounting a so-called "spectacular" -- a devastating attack with potential large loss of life -- before Christmas next month.

The attacks come at a delicate time for Northern Ireland's peace process.

The main Protestant and Catholic parties, which share power in the province's devolved assembly, are at loggerheads over when policing and justice responsibility should be transferred from London.

The threat from dissident paramilitary groups opposed to the peace process is at its highest for six years, according to the watchdog monitoring their activities, which called the situation "very serious".

Northern Ireland has been largely peaceful since the 1998 Good Friday agreement paved the way to power-sharing, after three decades of bloodshed between pro-British Protestants and Catholic opponents of British rule.

But the killings of two British soldiers and a police officer in March this year -- the first of their kind in about a decade -- highlighted the renewed threat posed by dissident paramilitary groups.

On September 8, army experts defused a 600-pound (270-kilo) roadside bomb near the Irish border, averting what police called a potential "devastating" explosion.

Three days later a car was damaged in an explosion carried out by dissident republicans outside the home of a police officer's parents, while a pipe bomb was made safe near the officer's sister's house.