Sinn Fein has rejected Unionist claims that mainstream Republicans are giving support to dissident bombers.

On Monday police discovered a bomb planted by dissident Republicans at Newtownbutler near the border in Co. Fermanagh. A senior police officer said he believed the device had been meant to kill his officers.

"I believe police officers were the intended target, but roadside bombs are indiscriminate," chief inspector Alywin Barton warned.

It is the third major dissident attack on police officers in Fermanagh in as many months.

Earlier this summer two police officers escaped serious injury when a bomb placed under a border bridge only partially exploded as they drove over it. Last month police escaped serious injury after dissidents failed in an attempted rocket attack on a PSNI foot patrol.

However, Ulster Unionist politician Tom Elliot angered Sinn Fein by claiming that dissident groups were getting assistance from mainstream Republicans and calling for the British Army to be redeployed along the border.

"You just don't carry these attacks out with a small group," he said. "Obviously the dissidents are being blamed, however I just believe there's a lot more of these people in the area in these operations than was maybe first envisaged by security forces."

Sinn Fein MP Michelle Gildernew rejected Elliot's claim.

"Those who engaged in this activity have little support and their actions will not advance Irish unity," she said. "Sinn Fein have a strategy for Irish unity and will not be deflected. However there is a clear cycle here exposed by Tom Elliot.

"Those who carried this act out are feeding off those Unionists who are trying to slow the pace of change and refuse to engage in a positive and constructive manner."

Meanwhile, Police Service of Northern Ireland (PSNI) Chief Constable Hugh Orde has played down speculation that he may be preparing to leave Northern Ireland to take over as Britain's most senior police officer as chief constable of London's Metropolitan Police.

Last week Ian Blair stood down as Met chief constable. Orde is being tipped as one of the favorites to take over from Blair.

But on Tuesday Orde signaled that he still had to years left on his contract as chief constable of the PSNI and said he remained determined to tackle the continued threat from dissident Republicans. He said he believed that dissident groups were now battling to see who could be the first group to kill a police officer.

"The threat from a small but determined group of dissident Republicans who have attempted to murder eight officers in the past six months will not detract us from our task of policing with all communities," he said. "In fact, the general outrage felt in the wake of recent attacks by dissident Republicans has strengthened relations between communities and the police."

Insisting that the Nationalist community was rejecting dissidents, he said, "Regardless of what community people come from and regardless of their background we hear a common theme, people want a police service which deals with local issues, addresses community concerns and makes streets and neighborhoods safer."