Lebanese troops have arrested Majid al-Majid, alleged leader of an al-Qaeda-linked Sunni Muslim group that claimed a double suicide bombing at the Iranian embassy in Beirut in November.
Fayez Ghosn, Lebanese defence minister, told AFP news agency on Wednesday that Majid, the so-called emir of the Abdullah Azzam Brigades, "was arrested by the intelligence services of the Lebanese army in Beirut".
He did not specify when the arrest took place.
"He was wanted by the Lebanese authorities and is currently being interrogated in secret," Ghosn said.
Al Jazeera's Rula Amin, reporting from Beirut, said Majid was wanted by the Saudis and Americans and his arrest was a major achievement for the authorities in Lebanon.
Saudi Arabia's Interior Ministry also confirmed that Majid, a Saudi citizen, was on a list of 85 suspects wanted by the kingdom.
The news of the arrest comes just days after Saudi Arabia pledged $3bn for the Lebanese army, in the largest grant ever given to the country's armed forces.
Lebanon's army is seen as one of the few institutions not overtaken by sectarian divisions that plague the country, but it is ill-equipped to deal with internal threats.
The Abdullah Azzam Brigades was designated in the US as a "terrorist organisation" in 2012, and has in the past claimed responsibility for firing rockets into Israel from Lebanon.
The group was formed in 2009 and is believed to have branches in both Lebanon and the Arabian Peninsula.
According to Islamist websites, Majid was revealed to be the leader of the Abdullah Azzam Brigades in 2012.
A Twitter account belonging to Sirajeddin Zreikat, a member of the group, appeared on Wednesday to have been suspended.
Zreikat had claimed responsibility in name of the Abdullah Azzam Brigades for the attack at the Iranian embassy in Beirut that killed 25 people.
He had given warning of more attacks in Lebanon if the Iran-allied Lebanese Shia group Hezbollah kept sending troops to support Syrian President Bashar al-Assad's government in its fight with Sunni-led rebels.
Palestinian camp clashes
In 2009, Lebanese authorities sentenced Majid in absentia to life in prison for belonging to a different armed group, the al-Qaeda-inspired Fatah al-Islam.
Fatah al-Islam was involved in heavy fighting with the Lebanese army in 2007 in the Palestinian Nahr al-Bared camp in northern Lebanon.
The clashes left more than 400 people, including 168 soldiers, dead.
After the fighting, many members of the group took refuge in the Ain al-Helweh Palestinian camp, which is believed to house numerous Sunni Muslim fighters.
A Palestinian official in the camp told AFP on Wednesday that Majid had left Ain al-Helweh in mid-2012 for Syria.
"With the war in Syria, we decided that [non-Palestinian] Arab citizens would not be allowed to remain in the camp, after information that jihadists were fighting alongside the rebels," the official said on condition of anonymity.
"He left the camp with five Saudis and Kuwaitis and they went to Syria. We didn't know that he had returned to Lebanon."