Israel said it carried out an air raid Friday that killed up to five Iran-backed militants it said were behind a rare rocket attack from across the border in Syria.
The strike came a day after Israel launched a dozen air raids on the Syrian-side of the occupied Golan Heights, raising concerns about a possible escalation.
Defence Minister Moshe Yaalon said Friday's raid hit members of a unit behind Thursday's rocket fire on the northern Galilee region and the zone Israel occupies on the Golan.
"Elimination of the squad which fired at Israel yesterday is further proof that we shall not tolerate any attempt to disrupt the lives of Israeli citizens or harm their security," Yaalon said in a statement.
"Those who want to do so should know that the Israeli military and security forces will pursue them to the end and get our hands on them, anytime and anywhere."
Prime Minister Benjamin Netanyahu said that it was his government's policy to "hurt anybody who tries to hurt us".
"We have no wish to escalate events but we are sticking by our policy," he said in a statement.
"The Israel Defence Forces hit the squad that carried out the fire and the Syrian forces which allowed it."
Syrian state television said five unarmed civilians were killed in Friday's raids, while an Israeli military source said "four or five" died in the strikes.
- 'Potential game-changer' -
Each side gave a different account of who was killed.
Syrian television identified them as unarmed civilians, the Israeli military source said they were members of the Palestinian Islamic Jihad militant group, and the Syrian Observatory for Human Rights monitoring group spoke of pro-regime National Defence Forces.
Israel earlier said that it hit 14 Syrian army positions in the Syrian-controlled sector of the Golan on Thursday night in response to the rocket attacks.
Previous cross-border fire has frequently been attributed to spillover from fighting inside Syria and to Islamist rebels holding ground close to the Israeli-held sector of the strategic plateau.
There has not been rocket fire from Syria at the Galilee for a long time, perhaps since the 1973 Arab-Israeli war known in Israel as Yom Kippur, Israeli media reported.
Analysts said it was a potential game-changer.
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"The message is clear: this is a new front, a new battleground," Eyal Zisser of Tel Aviv University told AFP.
"The assumption is that they want to send the message that a new front is open now that the situation on the ground is changing," said Shlomo Mofaz of the International Institute for Counter-Terrorism near Tel Aviv.
According to various sources, since January 2013 Israeli has launched deadly raids inside Syria targeting regime forces as well the Iran-backed Lebanese Shiite group Hezbollah.
Hezbollah, which helps the Syrian regime battle rebels, was the target of a deadly Israeli strike in January in which six of its fighters and an Iranian general were killed on the Syrian side of the Golan.
Several days later Hezbollah retaliated, killing two Israeli soldiers.
- Iran connection -
Yaalon said Thursday's attack came from positions under the control of President Bashar al-Assad's forces.
"The fire was carried out from territory controlled by the Assad regime, which allows terrorist activity against Israel and which we hold as also responsible," he said.
He said the actual assault was "carried out by a terrorist cell of Islamic Jihad, operated, funded and armed by Iran".
Iran is one of Assad's main backers and a supporter of the Islamic Jihad.
Though active in the Gaza Strip, the militant group has its headquarters in Damascus.
Israel's foreign ministry said on Friday that the Islamic Jihad force behind Thursday's rocket fire was under the operational command of an officer of the Iranian Revolutionary Guards Corps.
"We have credible information that the attack was carried out by the Palestinian Islamic Jihad organisation and was facilitated and directed by an Iranian operative, Saaed Izaadhi," ministry spokesman Emmanuel Nahshon said in a statement.
He said that Izaadhi headed a Palestinian unit in the Revolutionary Guards' elite Quds Force.
Israel seized 1,200 square kilometres (460 square miles) of the Golan from Syria in the 1967 Middle East war and annexed it 14 years later, in a move never recognised by the international community.