The Assistant Garda Commissioner for Organised and Serious Crime has described the arrest of Liam Byrne by Spanish authorities as "a blow" to the Kinahan Organised Crime Group.

The 42-year-old has been described in the High Court as heavily involved in drug trafficking and violent crime.

He was detained by Spanish police in a restaurant in Majorca on Sunday night while he was having a meal with family members, as part of an investigation headed by the UK's National Crime Agency (NCA).

The National Courts Office in Spain has confirmed that Byrne is not agreeing to his extradition to the UK to face charges for alleged firearms offences.

Assistant Garda Commissioner Justin Kelly has said the arrest is "a particularly significant development" because he said "Liam Byrne is a trusted member of the Kinahan Organised Crime Group and is well placed in the hierarchy."

Mr Kelly said the move represented "one step" in dismantling the Kinahan organisation.

Byrne's arrest came about following an intelligence led investigation into firearms offences by the NCA in the UK, supported by the Spanish National Police and gardaí.

Assistant Commissioner Kelly said it is "a real demonstration of our international co-operation with our partners, particularly the NCA and the Spanish authorities, who we have a lot of dealings.

"So absolutely, it's particularly significant and it's a blow to the Kinahan Organised Crime Group."

Mr Kelly also said the work targeting the group "continues unabated and that international cooperation continues on a practically daily basis."

And he said gardaí and other law enforcement agencies will work relentlessly to disrupt the Kinahan organisation.

"We have officers between the UK and Spain and now we have a Garda liaison officer based actually in the Middle East in Dubai, so all that work continues and we will be absolutely relentless in our work to disrupt this organised crime group."

A second man, Jack Kavanagh from Tamworth in England, was also arrested as part of the investigation.

The 22-year-old was detained at Malaga Airport in Spain while transiting from Dubai in the United Arab Emirates to Turkey.

The NCA said it obtained Trade and Co-operation Agreement (TACA) warrants after EncroChat messages showed the two men were believed to be involved in the supply and acquisition of firearms.

Asked today if Gardaí will be using the encrypted messaging platform as a tool to bring down criminal organisations, Assistant Commissioner Kelly said "obviously in public, I'm not going to talk about our exact strategies to take down these groups, but we use all forms of intelligence to feed our operations to take down that group."

He said the international operation showed that "there are no safe havens for criminals like Liam Byrne and we will continue that cooperation."

The NCA said Mr Byrne had flown into Palma Airport in Majorca from Dubai.

Asked if the authorities in the UAE had questions to answer as to why members of the Kinahan organised crime group, who are understood to be living in Dubai, have not been arrested, Mr Kelly said he was not going to comment publicly on what work has gone on in the background with the authorities in Dubai.

"But what I can say is that we have visited Dubai, we have been welcomed by the authorities there and we continue our work with them to achieve our goals with our international partners."

Assistant Commissioner Kelly also said Gardai are "completely satisfied" that they know the location of the senior members of the Kinahan gang but he said "it's not something I'm going to comment publicly on."