Nigerian President Muhammadu Buhari is ordering a probe into how an extremist Lebanese Muslim cleric, Ahmed al-Assir, got a visa to visit the country. The suspected terrorist was arrested Saturday by authorities at Beirut's airport while trying to flee to Nigeria via Cairo, Lebanese media reported.

Buhari, “furious” over the incident, has ordered his Foreign Ministry to investigate how a valid visa was issued to the Sunni Muslim extremist, who has been on the run for more than two years. Nigeria’s National Intelligence Agency and the embassy in Lebanon were also directed to explain what happened, a Foreign Ministry official told Vanguard Newspapers.

“The reported arrest of the wanted terrorist is a huge embarrassment to Nigeria, and the president has directed that the matter should be investigated,” the official told the Nigerian newspapers Tuesday. “We are amazed that such a high-profile terrorist would evade our radar. This is a major breach that cannot be allowed to go without investigation.”

June 2013 Abra battle A Lebanese army tank rolls past a mosque complex where radical cleric Ahmed al-Assir was believed to be sheltering with his supporters in Abra near Sidon, southern Lebanon, in 2013. Photo: Reuters/Ali Hashisho

Assir, who was apparently traveling with another man, attempted to flee Lebanon to Nigeria by way of Egypt with a forged Palestinian passport and a legitimate Nigerian visa through Beirut's Rafik Hariri International Airport. The captured militant leader is scheduled to appear Sept. 15 in a military court, according to the Daily Star in Beirut.

Assir is one of 71 suspects, including 24 fugitives, from a June 2013 battle with the Lebanese army in Sidon’s Abra neighborhood. He allegedly led the two-day fight, which killed 18 soldiers and about 40 Assir loyalists. The suspected terrorist is accused of murdering and attempting to murder soldiers and civilians, committing terrorist operations, possessing weapons and explosives, instigating sectarian tension and calling for sectarian warfare. If convicted, Assir and many other detainees could face the death penalty.

Assir also is known for his vocal criticism of Lebanon’s Shiite Hezbollah movement and Syrian President Bashar al-Assad. The firebrand Lebanese cleric was reportedly recruiting his followers to join the Islamic State group, also known as ISIS, and Sunni rebels fighting in Syria. A number of Assir loyalists have been detained since his arrest, according to Middle Eastern newspaper Al-Bawaba.