Rockets fired from Lebanon have struck northern Israel and triggered retaliatory artillery fire.
Two rockets fired from Lebanon struck northern Israel on Sunday, causing no injuries or damage, and Israel's military responded with artillery fire across the border, officials said.
The Lebanese rockets landed near the town of Kiryat Shmona, the military said, adding that it "responded with artillery fire towards the source of the launch".
Israeli Defence Minister Moshe Yaalon warned Beirut of even tougher reprisals on Sunday.
"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.
"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.
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.
A Reuters news agency witness in the Lebanon frontier area said more than 20 Israeli shells hit near two southern border towns.
The Israeli-Lebanese border has been largely quiet since Israel and the Lebanese Hezbollah militia fought a 34-day war in 2006.
But tensions spiked on the border between the two countries this month when Lebanese troops shot dead an Israeli soldier driving near the frontier on December 16. Officials suggested at the time that the shooting had been the isolated action of an individual.
A UN peacekeeping force met with both sides to restore calm after the incident. – Reuters and Sapa