The renewed focus on Iran by the Trump administration has spurred an outbreak of sabre-rattling in Lebanon and Israel and raised concerns that the calm that has existed along the border for more than a decade may be coming to an end.

In Lebanon, Hezbollah leader Hassan Nasrallah has warned that “there will be no red lines” in the next war with Israel and threatened to strike the Dimona nuclear reactor in the Negev desert and ammonia plants in Haifa with devastating results should Israel attack Lebanon.

In response, an Israeli government minister promised that “all Lebanon would be hit” if Hezbollah attacked the Israeli home front.

Since the last war between Hezbollah and Israel ended in August 2006, the border between the two countries has enjoyed its longest period of calm since the mid- 1960s but the inconclusive end to the 2006 conflict, when Hezbollah fought Israel to a standstill, has long fuelled expectations of a second round.

Even so, the calm endured — until the 2011 “Arab spring” upheaval and the war in Syria drew attention away from the Lebanon-Israel border.

The anti-Iran (and by extension anti-Hezbollah) rhetoric emanating from the White House has raised fears that another conflict may be building up.

However, both parties know that the scale of a new war will dwarf the 2006 conflict, a reality that has helped ensure a mutual deterrence.

Hezbollah has expanded enormously in terms of manpower, weaponry and experience in the last decade. Israel has retrained its army since its 2006 debacle and acquired new weapons and technologies.

The traditional theatre of conflict has long been limited to south Lebanon and northern Israel. Next time, the entire territories of both countries will be the battleground.

Israel will face barrages of missiles raining on its cities and towns as well as Hezbollah fighters storming across the border and possibly infiltrating by sea.

Lebanon will likely witness a level of destruction unseen since its 1975-90 civil war. Some Israeli strategists argue that in the next conflict Israel should treat all Lebanon as the enemy, rather than just Hezbollah, and target the trappings of the state such as infrastructure and the Lebanese Army.

“A war against Lebanon, which will inflict heavy damage on all of the country’s infrastructures, will spark an international outcry for a ceasefire after three days rather than after 33 days like in the second Lebanon war,” Giora Eiland, former head of Israel’s National Security Council, wrote recently in the Yedioth Ahranoth daily.

“It is only from a really short war that Israel will be able to emerge victorious and without serious damage to its home front.”

The flaw in Eiland’s analysis is contained in the second sentence. It presupposes that Hezbollah, cowed by the destruction unleashed on Lebanon, will simply stop fighting or bow to political pressure to halt the combat. But it is not in Hezbollah’s character to hand Israel victory on a plate. The Party of God has an interest in extending a war for as long as it can.

By prolonging the destruction in Lebanon, it would hope to foster international criticism of Israel, hasten diplomatic efforts to achieve a ceasefire on terms perhaps more beneficial to Hezbollah and allow the organisation more time to inflict damage on the Israeli military and Israel’s home front.

Israel’s population is unlikely to tolerate a war that brings normal life to a halt for weeks, placing tremendous pressure on the Israeli government to end the conflict.

The focus on Hezbollah in recent years has been on the party’s intervention in Syria rather than its 3-decade struggle against Israel. But Hezbollah’s leadership is acutely aware that an Israeli government may conclude that there will never be a better time to launch an offensive against its old enemy than while Hezbollah is fighting in Syria.

Hezbollah is still very focused on the front with Israel with many of its top fighters, especially anti-tank missile teams and rocket units, remaining in Lebanon rather than being deployed to Syria.

For two months, plain-clothes Hezbollah units have been conducting a thorough but low-key survey of the Israeli border, taking extensive measurements of terrain, including slope gradients, and photographing Israel’s new defences on the other side of the frontier fence, sources in south Lebanon say.

The survey, which is part operational planning and part psychological needling of Israeli troops, underlines that Hezbollah’s anti-Israel activities have not slowed despite the party’s heavy commitments in Syria.

Both Israel and Hezbollah repeatedly say that they do not want a war and that mutual deterrence remains strong. However, Israel has pushed the envelope more than Hezbollah in recent years with assassinations of key Hezbollah figures and air strikes against suspected arms depots or convoys carrying new weapons from Syria.

Hezbollah has been careful to tailor its reprisal operations so they do not upset the balance of terror but if another war does break out, it is likely to be the result of a miscalculation by one side or the other that quickly spirals out of control before either party can dial it back.