A security source told the Reuters news agency that a Syrian national suspected of being the leader of the cell had been found with six forged passports.
"He travelled to six Arab countries in 15 days. His group was planning several attacks against a wide range of targets," the source said.
The Lebanese military fought a fierce three-month battle in 2007 with members of the Fatah al-Islam group in the Nahr el-Bared refugee camp, which left more than 400 people dead.
Since then the group ha been accused of involvement in a number of deadly bomb attacks targeting the Lebanese army, but it was not clear if those arrested on Tuesday were suspected of links to Fatah al-Islam.
Yasmina Bouziane, a Unifil spokeswoman, told the AFP news agency that the peacekeeping mission was aware of the arrests.
"This is an issue that the Lebanese army and Lebanese authorities are addressing," she said. "It is a matter that is in the hands of the Lebanese authorities."
Troops with the United Nations Interim Force in Lebanon have been the target of several attacks since 2006.
The deadliest, which killed three Spanish and three Colombian peacekeeper, took place outside the Ain al-Helweh camp in June 2007.
Last week, 14 peacekeepers were injured by stone-throwing protestors while investigating the explosion of an arms cache in southern Lebanon.
Unifil, which currently has up to 13,000 troops, was set up in 1978 to monitor the border with Israel and was expanded after Israel's devastating war against Hezbollah in 2006.