The Lebanese authorities are reported to have arrested the head of a jihadist group that claimed the suicide bomb attack on Iran's embassy in November.
Defence Minister Fayez Ghosn told the AFP news agency that Majid al-Majid, the Saudi "emir" of the al-Qaeda-linked Abdullah Azzam Brigades, was being held by army intelligence in Beirut.
He later denied making any statement, but other sources confirmed the arrest.
The embassy attack killed 23 people, including the Iranian cultural attache.
A Salafist cleric close to the Abdullah Azzam Brigades, Sheikh Siraj al-Din Zureiqat, had issued a claim of responsibility in its name.
He warned attacks would continue in Lebanon until Iranian and Hezbollah forces stopped fighting alongside government forces in Syria, and the Sunni group's prisoners were released in Lebanon.
Investigators later identified the two suicide bombers as a Lebanese man with ties to hardline Sunni groups and a Palestinian man with ties to the fugitive Sunni Islamist cleric, Sheikh Ahmed al-Assir.
Mr Ghosn did not specify when the arrest of Majid al-Majid took place, according to AFP, which quoted him as saying: "He was wanted by the Lebanese authorities and is currently being interrogated in secret."
A Lebanese security source told the Reuters news agency that he had been captured with another Saudi militant and had been living in the southern city of Sidon.
Hezbollah's al-Manar TV cited security sources as saying that two attacks on army checkpoints outside Sidon on 15 December had been attempts to free him.
A soldier and four gunmen were killed in the ensuing clashes in the suburb of Majdelyoun, for which there was no claim of responsibility.
Majdelyoun is next to Ahmed al-Assir's stronghold of Abra, which the army captured in June after fierce clashes in which dozens of his supporters were killed.
Based in both Lebanon and the Arabian Peninsula, the Abdullah Azzam Brigades are named after a Palestinian jihadist ideologue who recruited mujahideen for the fight against the Soviets in Afghanistan in the 1980s.
The name was first used to claim a series of attacks against tourists in Egypt in 2004 and 2005, but the US government believes the group - which it has designated a terrorist entity - was not formed until 2009.
In Lebanon, the Abdullah Azzam Brigades is believed to have attracted hardline Islamist militants who had fought in the Iraqi insurgency and based itself in the Ein el-Hilweh Palestinian refugee camp, near Sidon.
The group began claiming responsibility for occasional rocket fire against northern Israel from 2009, but is not believed to have carried out any major attacks until November's Iranian embassy bombings.
The Abdullah Azzam Brigades were led by Saleh al-Qaraawi, a Saudi veteran of the Iraqi insurgency, until June 2012. He was succeeded by Majid al-Majid, a Saudi who like Qaraawi was named on Saudi Arabia's list of 85 most-wanted terrorists in 2009.
One Lebanese media report said he left for Syria a month ago, where he allegedly pledged allegiance to the leader of the al-Nusra Front, an al-Qaeda affiliate seeking to overthrow President Bashar Assad.