An Irish soldier on UN peacekeeping duty has been killed and three other soldiers injured in a gun attack in Lebanon.

It is understood an armoured vehicle the soldiers were in was surrounded by a mob and fired on while travelling to Beirut on Wednesday night.

Pte Seán Rooney, 23, was pronounced dead on arrival at a hospital near Sidon and another had surgery and is in a serious condition.

The other two soldiers are being treated for minor injuries.

They were members of the 121st Infantry Battalion, UNIFIL (United Nations Interim Force in Lebanon).

Pte Rooney, from Newtowncunningham in County Donegal, joined the Irish Defence Forces in March 2019.

The seriously injured soldier is Pte Shane Kearney, 22, from Killeagh in County Cork.

Irish Defence Minister Simon Coveney told RTÉ radio he understood two armourned patrol vehicles were on a standard administrative trip to Beirut.

"The two armoured vehicles effectively got separated, one of them got surrounded by a hostile mob – I think that’s the only way you could describe them - and shots were fired and unfortunately one of our peacekeepers was killed and another was very seriously injured," Mr Coveney said.

"I would have, of course, met a lot of these young men before they left when we had a troop review in Galway before they headed off on this mission – smart, bright and motivated, well-trained soldiers.  

"This is the worst possible news that a family can hear."

Taoiseach (Irish Prime Minister) Micheál Martin told RTÉ his sympathies were with the soldier's family.

"We know the commitment of our soldiers, particularly those in Lebanon. They take great pride in their work," he said.

"It has always been in the cause of peace and Ireland's international contribution."

He said it would be prudent to wait for a full investigation and analysis before discussing what happened.

Irish President Michael D Higgins said the dangers that come with peackeeping work should never be forgotten.

The chief of staff of the Irish Defence Forces, Lt Gen Seán Clancy, said: "Our thoughts are with his family, his friends and his fellow peacekeepers from the 121st Infantry Battalion.

"Our focus now is to ensure the safety and continued support for all our personnel deployed in Lebanon.”   

Senator Tom Clonan, a former army officer, said the route between the Irish Army's camp in southern Lebanon and the capital Beirut was well-known among the Irish who had served there.

He said since 2011 there had been a rise in the "levels of radicalisation".

"We've seen in parts of Lebanon and on the border with Syria, we have seen the rising of groups that are aligned with organisations like Islamic State," he said.

Sinn Féin leader Mary Lou McDonald said there is "deep pride in the role that our forces have played in peacekeeping missions for decades" and that the soldiers "are in our thoughts and prayers this morning".

Lebanon's caretaker Premier Najib Mikati expressed his deep regret over the incident and called for an investigation, urging all parties to "show wisdom and patience".

The Lebanese army also offered its condolences but did not give additional details on the incident.

A senior Hezbollah official, Wafiq Safa, said an "unintentional incident" had led to the peacekeeper's death and that the armed group was not involved.

Earlier in the year, the taoiseach visited troops serving in Lebanon and laid a wreath to the 47 members of the Defence Forces who had died while in service on peacekeeping duty there up to that point.

The Bishop of Raphoe, Alan McGuckian expressed his deep sadness at the passing of Pte Seán Rooney.

"With absolute commitment Seán has made the supreme sacrifice and has given his life in service of peace and reconciliation in our troubled world."

Ciara Feeney, who works in a local shop in Newtowncunningham, described Seán Rooney as someone "who would never stop smiling".

“Everyone in Newtown is at a stand-still," she said.

“It’s heart-breaking, a young soul gone too soon."

Kate Robinson, who owns Kate’s Kitchen in Newtowncunningham, said it is a "horrible day" for the village.

“It’s awful, he was only 23 years of age, this shouldn’t be happening.

“He was lovely, the most gorgeous fella, big tall fella and I can’t take it in.

“It’s going to be a horrendous Christmas for us, for everyone in the whole village, because all the young ones knew him."

Ms Robinson said it was Seán's dream to join the Irish army and he was very proud to serve.

“We will always remember him for being always happy and always smiling. “I feel for his mammy, his wee sister, his granny and his granda.

“It’s a horrible day.”