The Lebanese army has detained a main suspect in the killing of Irish peacekeeper Seán Rooney in a move coordinated with the powerful armed group Hezbollah, two security sources and a Hezbollah spokesperson said.
Private Rooney, 24, was killed on 14 December when the UN Interim Force in Lebanon (UNIFIL) vehicle he was travelling in was attacked near the village of Al-Aqbiya in the country's south, a stronghold of the Iran-backed group.
Pte Rooney's colleague, Trooper Shane Kearney, 23, suffered blunt force trauma to the head in the attack.
Hezbollah claim the detained man is a supporter of the militia and political party, but not a member of the group, a spokesperson for the group said.
The security sources said the man was suspected of firing shots at the UNIFIL vehicle that was travelling through south Lebanon on 14.
UNIFIL acts as a buffer between Lebanon and Israel and operates near the border.
"The main shooter has been arrested by security forces after Hezbollah handed him over hours ago," a security official said, declining to be identified because he was not authorised to speak to the media.
Hezbollah is cooperating in the probe led by Lebanese military intelligence, the official said, adding that "preliminary investigations are nearly complete".
The Irish Defence Forces said: "There are three investigations currently ongoing into this incident.
"As these investigations are currently ongoing, the Defence Forces has no further comment to make at this time."
Earlier this week, a judicial official said that Lebanese investigators had identified suspects in the attack, adding that there were "at least two" gunmen.
A car carrying armed men followed the UNIFIL vehicle, the judicial source had said, citing preliminary findings and calling the attack "premeditated".
Hezbollah has repeatedly denied involvement in the incident, and its security chief Wafic Safa has described the killing as "unintentional".
Witnesses said villagers in the Al-Aqbiya area blocked Private Rooney's vehicle after it took a road along the Mediterranean coast not normally used by UNIFIL.
Al-Aqbiya is just outside UNIFIL's area of operations, the force said.
The three passengers were injured when the vehicle hit a pylon and overturned.
Over the years, there have been a number of incidents between Hezbollah supporters and UN peacekeepers but they have rarely escalated.
UNIFIL has urged Beirut to ensure a swift investigation into the first violent death of one of its peacekeepers in nearly eight years.
UN 'heartened by Lebanese support'
In a statement, the UN declined to comment on reports that of an arrest.
A spokesperson said there is an "ongoing investigation into this tragic incident, therefore we can't pre-empt its results and we need to protect the outcome of the investigation".
They added: "This incident was deeply shocking, a crime against UNIFIL peacekeepers who have travelled from far to work in preserving stability in a volatile environment and to work in support of the local population.
"We have asked to find out what happened, and for the perpetrators to be brought to justice.
"And we ask that people refrain from sharing harmful information, because disinformation is the fuel on which the fire of violence can spark.
"We need swift and effective investigations to find those responsible and hold them accountable for their crimes.
"We are heartened by the support of the Lebanese authorities and leaders from across the political spectrum, and we are hopeful that we can get to the truth."
UNIFIL was set up in 1978 to monitor the withdrawal of Israeli forces after they invaded Lebanon, in reprisal for a Palestinian attack.
Israel withdrew from south Lebanon in 2000 but fought a devastating 2006 war with Hezbollah and its allies. Lebanon and Israel remain technically at war.
