Andrea Tenenti, a spokeswoman for the U.N. Interim Force in Lebanon, said a forensics team was on scene near the southern city of Tyre working with members of the Lebanese military.
"Five peacekeepers were injured," she said in a statement. "They were treated at the location and were later evacuated for further medical treatment."
No group claimed responsibility for the explosive attack. The incident isn't uncommon in southern Lebanon.
It comes as Lebanese officials told U.S. lawmakers that Beirut needed more help in funding national security forces. Lebanon's finance minister said that a strong national army meant Hezbollah would lose its reason for maintaining a military arsenal.
U.S. officials have said Washington was committed to helping Lebanon with border security. Beirut has issued several complaints with the United Nations over alleged Israeli border violations while concerns grow over civil war in neighboring Syria.
Last month, UNIFIL sent more troops to the southern Lebanese border after Katysusha rockets were fired on Israel from Lebanese territory. Israeli forces responded by firing six heavy artillery shells near the border region.