Israeli aircraft have carried out a raid in southern Lebanon just hours after a civilian was killed in northern Israel by shell-fire blamed on Hezbollah guerrillas.
A 16-year-old Israeli boy was killed in Shlomi
There is no word so far on casualties or damage as a result of the Israeli action, which Lebanese police said targeted a position near the village of Tayr Harfa.
Earlier, an Israeli teenager was killed and four other people injured when shells landed in the northern Israeli town of Shlomi, near the border with Lebanon.
The 16-year old boy who died was the first Israeli civilian in the area to be killed in such action since Israeli forces pulled out of southern Lebanon three years ago, ending more than 20 years of occupation.
Correspondents say the death will be seen in Israel as a severe escalation.
Israeli medical and army sources said Hezbollah deliberately fired into the settlement.
But a Hezbollah statement said its fighters had been targeting Israeli jets violating Lebanese airspace.
Tensions have risen sharply in the disputed border area in recent days after a period of relative calm.
Friday saw clashes between Israeli troops and Hezbollah in the Shebaa Farms area, further east.
"This is a clear provocation by Hezbollah and Israel will not
sit idly by," said Israeli Government spokesman Avi Pazner after Shlomi came under fire.
The Israeli security cabinet is expected to meet on Sunday evening.
The BBC's Kim Ghattas in the Lebanese capital Beirut says the question there now is whether Israeli retaliation will be limited to just one raid.
Another Israeli official, David Granit, said Israel was considering a request for an emergency meeting of the UN Security Council.
Israeli military sources confirmed anti-aircraft fire had been reported in the border area at around 1230 (0930 GMT).
Although the border had been generally quiet since the beginning of the year, tensions have worsened recently with a number of incidents since Friday.
This escalation comes after a Hezbollah fighter was killed in a car bomb in the suburbs of the Lebanese capital Beirut last week - an incident the group blamed on Israel and vowed to avenge.
Hezbollah, which is backed by Iran and Syria, routinely responds to Israeli air force flights over
Lebanon with anti-aircraft fire.
But our correspondent in Beirut says that depending on the direction in which these guns are aimed, shrapnel sometimes ends up in Israel itself.
Warning to backers
Israeli Foreign Minister Silvan Shalom demanded on Sunday that Syria and Lebanon restrain Hezbollah militants.
"We say to Syria and Lebanon as responsible parties for Hezbollah behaviour... that if Hezbollah activities
continue and constitute an undermining of security of the citizens of Israel, we will have no choice but to defend ourselves," he said on Israel radio.
"I think the regime in Syria knows very well what our capabilities are, and I don't think it's worthwhile for it to put us to the test."
But Hezbollah chief for south Lebanon,
Sheikh Nabil Qauq indicated there would be no end to its actions against Israeli forces in the Shebaa area and Israeli military overflights.
"The resistance is capable of responding to Israel's violations
and provocations," he said.