Two rockets have been fired into northern Israel from Lebanon.
The Israeli military responded with eight shells fired into a fruit plantation near the city of Tyre, reports said.
Remnants of a Katyusha rocket were found in Israel, police said. There were no reports of casualties.
Israel and the Lebanese militant and political group Hezbollah fought a devastating 34-day war across the border in 2006.
Israeli resident Ephraim Gold, who heard the sound of up to six explosions in the city of Nahariya – some 6 miles (9.6km) from the border with Lebanon – told the BBC that the rockets had sparked panic.
“People were screaming, running away,” he said. “It’s been quiet here for so long, this was completely unexpected.
“The sirens went off. Everybody is in bunkers. The children had to leave their schools.”
He said Israeli troops were in the area to investigate the source of the attacks.
Both UN peacekeepers in Lebanon, who have a remit to monitor the Israeli border, and the Lebanese army deployed extra troops following the rocket launches, a UN spokeswoman said.
Israelis respond and drag rocket remnants from the ground
Unifil (the UN Interim Force in Lebanon) said: “Unifil is in contact with both sides, urging them to exercise maximum restraint, uphold the cessations of hostilities and avoid taking steps which would lead to further escalation.”
Unifil was set up in 1978 after Israel invaded Lebanon, and was expanded after Israel’s 2006 war with Hezbollah.
The 2006 war was triggered by a Hezbollah raid into Israel, in which the group seized two soldiers and killed others.
On the Lebanese side more than 1,000 people died, mostly civilians. About 160 Israelis – most of them soldiers – died in the fighting and rocket fire.
The border has been tense, but largely quiet. There have been occasional clashes and rocket fire. The Associated Press says this is the fourth such attack in 2009.
Palestinian militant groups operating in Lebanon are often blamed.
spotted by RS