Israel launched air raids against Syrian army positions early Wednesday and issued a stark warning to Damascus just hours after a bomb on the occupied Golan Heights wounded four Israeli soldiers.
The Syrian army said one soldier was killed and seven wounded in strikes on its bases in the Quneitra region, which it denounced as "acts of aggression" that endangered regional stability.
The bombing marked the most serious escalation along the ceasefire line with Syria since the 1973 Middle East War, with Israel's defence minister warning that Damascus would pay a "high price" for helping militants bent on harming the Jewish state.
Although there was no claim of responsibility for Tuesday's roadside bomb attack which targeted soldiers patrolling the Israel-Syria ceasefire line, Israel has raised the alarm about increased activity there by Lebanon's Hezbollah, calling it a "new threat".
Militants from the powerful Shiite movement, who fought a bloody war with Israel in 2006, are now fighting alongside the Syrian army against rebels seeking to overthrow the Damascus regime of President Bashar al-Assad.
After the Golan attack, Prime Minister Benjamin Netanyahu warned that Israel would act "forcefully" to defend itself, with the air force making good on his pledge several hours later.
The pre-dawn strikes targeted a Syrian army training facility, a military headquarters and artillery batteries, the Israeli army said.
"Our policy is clear: we hurt those who hurt us," Netanyahu told ministers.
US State Department spokeswoman Jen Psaki backed Israel's right to self-defence.
"Assad's desperate efforts to cling to power increases the propensity for spillover violence," she told reporters in Washington. "Israel has a right to defend itself."
"We continue to call upon the regime to avoid any action that would jeopardise the long-held ceasefire between Israel and Syria."
Tuesday's attack, which injured four paratroopers, one severely, was the third such incident in two weeks along Israel's northern frontiers.
Two previous attempts to strike soldiers along Israel's northern borders on March 5 and March 14 were blamed on Hezbollah.
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- 'Israel shouldn't interfere' -
"We see the Assad regime as responsible for what is happening under its authority, and if it continues to cooperate with terror elements who seek to harm Israel, we will make it pay a high price," Defence Minister Moshe Yaalon said in a statement.
"We will react with determination and force against anyone operating against us, at any time and any place, as we have done tonight," he said.
Calm returned following the strikes, although three Israeli tanks could be seen along the ceasefire line, just southeast of Majdal Shams, an AFP correspondent said.
In the town, which is populated by Druze residents many of whom are fiercly loyal to Damascus, there was anger at the Israeli raids.
"It was an unacceptable act," said Ali Abu Saleh, a man in his 30s with an outsized moustache, accusing Israel of trying to topple Assad.
"Israel has no right to strike inside Syria," agreed bookshop owner Sagar Abu Slah. "It's a Syrian internal war. Israel shouldn't interfere but nor should Hezbollah."
Israel, which is technically at war with Syria, seized 1,200 square kilometres (460 square miles) of the Golan Heights plateau during the 1967 Six-Day War and later annexed it in a move never recognised by the international community.
Since the Syrian conflict erupted in 2011, the plateau has been tense, with a growing number of stray projectiles hitting the Israeli side, prompting an occasional armed response.
But the recent attempts to harm soldiers has raised fears that years of calm which have prevailed along Israel's northern frontiers may soon end.
"There has been no such series of events in the north since the Second Lebanon War in 2006," said Haaretz newspaper, linking the surge in attacks to a February 24 air strike which targeted a Hezbollah position in Lebanon, which the group blamed on Israel.
If the current escalation continues, Israel was liable to be drawn into "a more forceful response," the paper said, suggesting the military may have to "set a higher price tag" for such attacks.
Yediot Aharonot took a similar line, saying Israel should consider sending a clear message in the form of "one or several hammers that will pound Damascus or Beirut powerfully and shake up somebody over there".
"A policy of 'sit-still-and-do-nothing'... is an invitation to the next incident."