Israeli soldiers made a brief incursion at the weekend into Lebanon near the disputed Shebaa Farms territory, the Lebanese army said on Monday.
"A group of five Israeli soldiers on Sunday evening entered 150 metres (yards) inside the area of al-Shaal, east of Kfar Shouba (in southeastern Lebanon) and remained in the area for 10 minutes before leaving," an army statement said.
It called the move "a blatant and repeated breach of Lebanese sovereignty."
The army has informed the UN peacekeeping mission in southern Lebanon of the incident, an army official told AFP.
Yasmina Bouziane, spokeswoman for the United Nations Interim Force in Lebanon (UNIFIL), told AFP that the UN was investigating the incident.
"A joint UNIFIL-Lebanese army investigation team was sent east of Kfar Shouba to look into the circumstances of an alleged IDF (Israeli Defence Force) Blue line violation," Bouziane said, referring to the demarcation line between the two countries.
"The investigation is still ongoing and UNIFIL is in touch with both parties to clarify the matter."
Israeli jets regularly violate Lebanese airspace, but it is rare for a land or naval violation to take place.
An Israeli warship entered Lebanese waters on March 18 before being intercepted by UN naval forces.
The overflights have drawn criticism from Lebanese authorities and the international community as they are in violation of UN Resolution 1701, which ended the 2006 war between the militant group Hezbollah and Israel.
Tensions have risen along the Lebanese-Israeli border since a declaration of "open war" by Hezbollah chief Hassan Nasrallah after the February assassination of top Hezbollah operative Imad Mughniyeh in Damascus.
Hezbollah blamed Israel for the killing, but it denied any involvement.
Israel held a five-day nationwide military exercise earlier this month simulating air and missile attacks on the country. Lebanese troops were put on alert despite Israeli Prime Minister Ehud Olmert's assurances that there was "nothing hidden behind" the drills.