Prime Minister Benjamin Netanyahu accused Hezbollah of being involved in firing rockets at Israel on Sunday, as his government warned Beirut of even tougher reprisals after the army shelled Lebanon.
The Israeli leader's remarks came after his country's army fired about 20 shells into southern Lebanon without causing any damage, after rockets were launched in the opposite direction.
Netanyahu said the Shiite movement "Hezbollah deploys thousands of rockets and missiles among the civilian population. So it is committing a double war crime under the patronage of the Lebanese government and its army, who do nothing".
"We know that Iran, which continues to help the Syrian government to commit massacres against its people and arm terrorist organisations abroad, is behind Hezbollah," the statement from his office charged.
Israeli Defence Minister Moshe Yaalon warned the Lebanese government of an even tougher response to further rocket attacks.
"We will not tolerate fire from Lebanon on our territory... We consider the Lebanese government and army responsible for this morning's fire," said Yaalon.
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"The Israeli army responded by firing a large number of shells at the area from where the rockets were fired. If necessary, it will be even tougher.
"I would never advise anyone to test our patience and our determination to defend the security of the Israeli people," the minister said in a statement.
His remarks came after the army said five rockets were fired at Israel, with at least one of them exploding on its territory without causing any casualties or damage.
In retaliation, the Israeli military fired about 20 shells at Lebanon, also without causing any casualties or damage, according to a Lebanese security official.
Tension has spiked on the border between the two countries since Lebanese troops shot dead an Israeli soldier driving near the frontier on December 16.
It was the most serious incident along the border since 2010, when one Israeli soldier and two Lebanese soldiers, and a journalist were killed.
Israel's border with Lebanon has been largely quiet since the 2006 war with Hezbollah.