Two vehicles occupied by five people armed with assault rifles blocked the UNIFIL patrol for a few minutes on the night of March 30-31, "denying UNIFIL its freedom of movement," UN Assistant Secretary-general Angela Kane said.
The patrol challenged the gunmen who left before they could be identified, Kane said in a monthly Middle East report to the council.
"This was the first such incident since the end of the 2006 war that UNIFIL came across armed elements in its area of operations," she said.
'Cause for concern'
In Lebanon, UNIFIL spokeswoman Yasmina Bouziane said the incident began when the UNIFIL patrol saw a "suspicious" pickup truck towing a trailer and began to follow it.
Kane said that since the incident UNIFIL and the Lebanese army had introduced new measures, including patrols and checkpoints, to ensure unauthorized armed personnel were not present and stop weapons being moved into southern Lebanon.
The March incident took place in the vicinity of Jibal al-Butm, near the coastal city of Tyre. The area has a strong Hizbullah presence.
The incident also was mentioned by U.N. Secretary-General Ban Ki-moon in a regular report on Lebanon this week. He said it was a serious violation of Security Council resolutions that "gives cause for concern."