Minister for Foreign Affairs Micheál Martin has said he is extremely concerned at the serious security situation in Northern Ireland.

He also condemned recent attacks against the police, blamed on dissident groups.

Mr Martin said he hoped this Saturday's Apprentice Boys of Derry marches, including a controversial feeder parade in Ardoyne, would take place in a calm and peaceful atmosphere.

After a series of bomb attacks blamed on dissident republicans, the minister called for an immediate end to the targeting of PSNI officers and in particular Catholic officers.

He also called for political and community leaders and the family, friends and communities of PSNI officers to give them their full and unreserved support.

A spokesman for the minister also denied a claim by Northern Ireland Deputy First Minister Martin McGuinness that the Government and the British authorities had been involved in secret talks with dissident republicans.

The Northern Ireland Office repeated the Secretary of State's position that meaningful talks could not be held with people who were not committed to peaceful means of pursuing their goals.

Mr McGuinness told BBC Radio Ulster: 'I encourage dialogue, I think it is important.

'I do understand the governments will come out and say that this isn't true, it isn't happening, and they have all sorts of mechanisms and phrases to use which cover themselves, but the reality is that some of these dissident groups, I know for a fact, have been involved in discussions with both the Irish and the British government in recent times.'

Last week Northern Secretary Owen Paterson denied talks were taking place.

'You cannot have any meaningful talks with people who are not committed to peaceful means,' he said.

'They are not listening. They are disparate. They are a very small armed group with no discipline or clear focus on where they are going.'

Police search farmland after tractor find

Police have searched farmland and roads near Sixmilecross in Co Tyrone to determine whether a bomb may have been attached to a magnet discovered under a tractor.

It is understood the magnet was found when the farmer, a former member of the security forces, left his tractor in for servicing on Monday.

It is not known how long it had been in place.

The PSNI says nothing untoward has been found but their inquiries are continuing.

In the last week three booby-trap bombs have been found under the vehicles of security force members in Bangor, Kilkeel and Cookstown.