Lebanon's army is deployed in south Lebanon along with a UN force
The Hezbollah political and militant group has described the shooting down of an army helicopter in south Lebanon as "tragic and painful".
But the Shia movement has not confirmed local media reports that the gunmen were its members. The attackers' motive remains unclear.
One of the pilots was killed and the helicopter was forced to crash-land.
The attack on the helicopter took place in an area of south Lebanon where Hezbollah is known to have a presence.
A leading Lebanese newspaper has said that Hezbollah gunmen mistakenly fired at the army helicopter.
The government has not yet commented on the incident.
A memorial service has been held for the officer killed in the incident, Samer Hanna. He was due to be buried in his home town, Tanoureen, later on Friday.
As part of the ceasefire deal that ended the 2006 war between Hezbollah and Israel, the Lebanese army deployed in southern Lebanon along with a strengthened United Nations peacekeeping force.
Hezbollah's continued deployment in southern Lebanon and its holding on to its weapons are highly controversial issues.
The movement is militarily far stronger than the Lebanese national army.
But a policy statement by Lebanon's national unity government recognises Hezbollah's right to use all means possible to "liberate" Lebanese land that Lebanon says is occupied by Israel.