Lebanese troops found and dismantled four rockets ready for launching near the border with Israel on Wednesday, said a senior Lebanese army official.

The discovery comes one day after a Katyusha rocket fired from Lebanon exploded in the Upper Galilee, marking the first such incident since last month.

The attack on Tuesday drew a rapid response from Israeli artillery in a brief flare-up across the border that caused no casualties.

The Lebanese official said the rockets were discovered Wednesday, placed in a building under construction in the Houla area from where Tuesday's rocket was launched.

He says three of the four Katyusha rockets found were ready to be fired. He spoke on condition of anonymity in line with military regulations.

Opposition leader and Kadima chairwoman Tzipi Livni said on Wednesday morning that "Lebanon is responsible for everything that takes place in its territory." Livni told Israel Radio that Israel must send an unequivocal message that it will not accept rocket fire along its northern front.

Nine Katyushas have struck northern Israel since the Second Lebanon War in 2006, however the Lebanon-Israel border has been largely quiet since Israel and the militant Hezbollah group fought a bitter war in 2006.

The rocket which was fired on Tuesday hit an open field near Kiryat Shemona and caused no casualties. A Lebanese security official confirmed that the rocket was fired from the Houla village in southern Lebanon, near where the United Nations has investigated Lebanese charges that Israel planted spy devices then subsequently exploded them last week.

There were no immediate claims of responsibility for the shooting.

The Israel Defense Forces fired artillery rounds at Houla in response to the attack, both IDF and Lebanese officials said. An IDF spokesman said that the army viewed the attack with "utmost severity," adding that Israel was holding Lebanon responsible for the incident.

Hours before the attack, Defense Minister Ehud Barak toured the north and spoke of Israel's desire to maintain the relative quiet in that area of the country.

"We have nine years of quiet in the north that were interrupted for a number of painful weeks for the Second Lebanon War," the defense minister said, referring to the month-long war against Hezbollah guerillas. "We are preparing for all other possibilities, including the possibility that they will subject the towns of the north to another test."

Kiryat Shmona resident, Avishay Sabti, said he heard a loud explosion at around 6:45 P.M on Tuesday evening. "As someone who has lived in Kiryat Shmona, I have experience in these instances," Sabti said. "I immediately took cover, but I understood after a few minutes that this was just a lone [rocket] fired."

Sabti said a siren was heard before the rocket exploded. He added that the town continues to function as it would on a normal day. There are people in the streets and the residents have not been instructed to take cover in shelters, Sabti said.

Last month, two Katyushas struck the Western Galilee, leading Israel to file a complaint with the United Nations. The Israel Defense Forces fired retaliatory artillery at southern Lebanon in reponse to the rocket fire in September, as well.

The incident in September was the first time since February that rockets had been fired from Lebanon into Israel, raising tensions along a border that remains volatile three years after a war between Israel and Hezbollah guerrillas in Lebanon.

Israel believes that Hezbollah has been stockpiling its weapons cache at an enormous rate since the 2006 war. Israeli estimates have put the cache between 40,000 and 80,000.

Earlier this month, a shell exploded at the home of a senior Hezbollah official. Hezbollah denied reports that the official had been killed in the blast, which Israel said proved the guerilla group to be in violation of a United Nations-brokered truce.

Not long after, a United Nations investigation into the explosions indicated that Israel may have planted spy devices on Lebanese land in what a senior UN official said would be a violation of a cease-fire agreement.

The UNIFIL peacekeeping force in Lebanon said its preliminary probe into two explosions in the south showed they had been caused by the detonation of underground sensor devices.

The units were apparently buried by Israel Defense Forces troops during the 2006 war with the Lebanese Shi'ite group Hezbollah, it said.