Israeli forces fired artillery into the border region with Lebanon on Tuesday in response to a rocket attack, the Israeli Army said.
“Two rockets were fired from Lebanon towards northern Israel. One of the rockets was intercepted by the Iron Dome aerial defence system and the second rocket fell in an open area inside Israel,” the military said on its Twitter account.
In response, it said, Israeli artillery struck Lebanon.
The United Nations Interim Force in Lebanon (Unifil) said it had launched an investigation into both attacks and called for calm.
“Unifil radars detected at 4.30am [local time] a rocket launch from a region lying to the north-west of Al Qlayleh village [in south Lebanon] towards Israel,” the statement said. “Later, our radars detected Israeli artillery fire in response.”
Unifil said it was in contact with both sides to urge maximum restraint and avoid escalation.
“We have boosted security in the region, along with the Lebanese Army, and launched an investigation,” the UN forces said.
While no group claimed responsibility for the attack, Lebanese Army sources said Palestinian groups were behind the rocket attack.
The Lebanese Army said the area of Wadi Hamoul was targeted by a dozen 155mm artillery shells.
Israeli Defence Minister Benny Gantz said the economic crisis in Lebanon could lead to more exchanges of fire.
“We will not allow the social, political and economic crisis in Lebanon to turn into a security threat to Israel. I call on the international community to take action to restore stability in Lebanon,” he said in a tweet.
The Israeli military Chief of the General Staff General Aviv Kohavi said in a visit to the border area that Israel “would respond both overtly and covertly to any violation from Lebanon, whoever it may be”.
Rockets were fired from Lebanon into Israel in May, during the 11-day conflict between Israel and armed Palestinian groups in the Gaza Strip.
Rocket fire from Lebanon into Israel is rare, with few outbreaks of violence since Israel fought a month-long war against Hezbollah in 2006.
Meanwhile, Syria's air defences intercepted an Israeli attack on the Al Safirah area of southern Aleppo on Monday, Syrian state media reported. The area has been hit by Israel repeatedly because of reports of a growing Iranian presence.
A Syrian military spokesman said the damage was being assessed after air defences shot down most of the missiles, which were aimed at unspecified locations.
Syrian opposition forces claimed the air strikes were aimed at Iranian Islamic Revolutionary Guard Corps bases and a weapons plant, in a continuation of Israeli attacks against Iranian military research and development infrastructure over the past year.
British-based monitor Syrian Observatory for Human Rights said two Syrian fighters and three non-Syrians were killed.
The Syrian government has never directly acknowledged that strikes were aimed at Iranian assets.
However, Syrian military sources told Reuters that Iran has a strong presence in the province in northern Syria, including IRGC officers at the Kuweires military airbase, 30 kilometres to the east of Aleppo.
An Israeli Army representative said the Israeli military does not comment on foreign reports, but officials previously said earlier missile strikes had slowed Iran’s entrenchment in Syria.
Explosions were heard across Aleppo, which was Syria's most populated urban centre and a commercial and industrial powerhouse before the war
Authorities said work was under way to repair the main electricity cable to the city after a direct hit cut power.
The air strikes were the first since a new Israeli government led by Naftali Bennett came to power last month.
Mr Bennett vowed to maintain his predecessor Benjamin Netanyahu's policy of containment of Iran's military expansion in Syria. Israel's establishment said this expansion upset the region's strategic balance.
Western intelligence sources said Israeli strikes on Syria are part of a shadow war approved by the US and a policy to undermine Iran's military power without triggering a major escalation of hostilities.
Washington recently carried out strikes against installations belonging to Iran-backed militias in eastern Syria in response to rocket attacks against US interests in Iraq.
The Pentagon this month said it was deeply concerned about a series of retaliatory attacks on US personnel based in the north-east of the country, who came under fire from Iranian-backed militias operating in the area that borders Iraq.
Iran-backed militias are a growing presence across Syria after helping Syrian President Bashar Al Assad regain territory lost to insurgents.