A previously unknown militant Islamic group claimed responsibility Monday for a weekend rocket attack on northern Israel.

The self-proclaimed ''Jihadi Badr Brigades - Lebanon branch,'' vowed in a statement faxed to The Associated Press in Beirut to continue attacks.

''We had promised our people jihad (holy war),'' the statement said. ''Here, we again strike the Zionists when a group from the Jihadi Badr Brigades struck the Zionists in the occupied Palestinian territory.''

At least two rockets fired from Lebanon landed Sunday in the northern Israeli town of Kiryat Shemona, causing damage but no casualties. It was the first time rockets were fired from Lebanese territory at the Jewish state since last year's war between Israel and Hezbollah guerrillas in Lebanon.

Both the Lebanese army and the U.N. peacekeeping force in southern Lebanon condemned Sunday's incident as a serious violation of a U.N.-brokered cease-fire that ended last year's war.

The militant group said it fired two Katyusha rockets toward ''the occupied interior of our beloved land from the beloved south which is standing fast in the face of all Zionist conspiracies and arrogance.''

''We affirm that we will continue (attacks on Israel) no matter what the sacrifices on the jihad path are,'' the statement added.

The authenticity of the claim could not be immediately confirmed.

The statement, dated June 17, began with a Quranic verse and carried a picture of Jerusalem's Dome of the Rock with a Palestinian flag in the background.

The Lebanese army said in a statement that three 107 mm Katyusha rockets were fired at Israel by ''unknown elements'' and that a search was under way to find the attackers. Troops sent to search the suspected launching area found a fourth rocket equipped with a timer. The army said one the rockets landed in a border area.

Hezbollah had denied any involvement in Sunday's attack. So did a radical Palestinian group, the Syrian-based Popular Front for the Liberation of Palestine-General Command, which had in the past been blamed for firing rockets at Israel.

Prime Minister Fuad Saniora said the attack was geared at undermining the stability of Lebanon and vowed to apprehend and prosecute the perpetrators.

''The state ... will spare no effort in uncovering those who stand behind this incident, which is aimed at attempting to undermine the stability'' of Lebanon, Saniora said Sunday.

Russian Ambassador Sergei Boukin voiced concern about Sunday's incident, saying his country voted for the U.N. Security Council resolution that ended last year's war.

''We consider any violation of this resolution unacceptable at all,'' Boukin told reporters after meeting Saniora.

The 2006 conflict started with a cross-border raid by Hezbollah in which three Israeli soldiers were killed and two captured. Israel launched an air offensive against Hezbollah targets and Lebanese infrastructure. The war ended inconclusively after 34 days.