In Beirut the feeling of safety was always relative, said a 55-year-old resident of the Lebanese capital.

"Even before this week's attack, there were always Israeli reconnaissance planes flying overhead. But this strike was painful because it was in a residential area," the accountant told DW, referring to the drone strike that killed a senior Hamas member, Saleh Arouri, on Tuesday night.

Israel has not directly confirmed it was responsible but has said that as part of its battle against Hamas in Gaza, it would try to "eliminate" Hamas leaders wherever they were.

"We do feel less safe right now," confirmed a 30-year-old teacher living in Beirut. "We don't know if we might get bombed at any time."

Despite their fears, none of the Beirut residents DW spoke with — all of whom spoke on condition of anonymity because of the sensitive nature of the topic in their city — wanted Lebanon's powerful Hezbollah militia to go to war with Israel as a result. They certainly didn't want a regional war either, they insisted.

A retail assistant, 45, in Beirut believes Hezbollah provides a useful deterrent that prevents the Israel military from entering Lebanon. "They're the only ones working to protect us," she told DW.

"But nobody likes war," the teacher added. "I'd like them [Hezbollah] to be cautious."

An important speech

This is why all eyes were on Hezbollah leader Hassan Nasrallah on Wednesday evening as he gave a speech the day after the alleged Israeli assassination in Beirut.

In his speech, Nasrallah called the killing "a major dangerous crime." But he made no concrete threats about escalation.

Nasrallah's comments were hard to interpret. Some longtime Hezbollah observers suggested his tone was more aggressive than in previous speeches. Others, including Lebanese Foreign Minister Abdallah Bou Habib, seemed to think that Hezbollah, one of the most important political forces in his country, were unlikely to declare all-out war on Israel.

"We hope they don't commit themselves to a larger war… We have a lot of reasons to think that this will not happen," Bou Habib told US news channel CNN this week. Nobody in Lebanon wants this, he added — including, he suspected, Hezbollah.

In 2006, the Israeli military and Hezbollah fought a damaging 34-day war in Lebanon after Hezbollah abducted several Israeli soldiers. Millions were displaced, over 1,000 were killed and Lebanese infrastructure was badly damaged. The fight essentially ended in a stalemate and an Israeli withdrawal.

Since 2006, "Hezbollah has massively expanded its arsenal and the sophistication of its weaponry," Jeffrey Feltman, a visiting foreign policy fellow at the US think tank, the Brookings Institution, said in a November commentary. "The irreducible purpose of Hezbollah's estimated 150,000 rockets is to deter Israel from a massive attack on Iran — or to retaliate for a massive Israeli attack on Iran."

Rules of engagement breached

Since 2006, the two sworn enemies have regularly engaged in tit-for-tat exchanges of rockets on Lebanon's southern border. That's a regular occurrence, experts say, and indicates that both sides apparently accept the unofficial rules of engagement based around deterrence.

This summer, Israeli Prime Minister Benjamin Netanyahu explicitly threatened to kill Arouri, several months before the October 7 terror attacks on Israel by Hamas.

Hamas is classified as a terrorist organization by the US, EU, Israel and other governments. Hezbollah is also designated as a terrorist organization by several countries, including the US and Germany, although the classification is considered controversial by some because of the role Hezbollah's political wing has played in successive Lebanese governments since 1992.

In response to Netanyahu's comments, Hezbollah leader Nasrallah declared that these kinds of assassinations were a red line for his organization, no matter who they targeted. 

The latest alleged Israeli assassination-by-drone in the middle of a crowded city suburb, over 100 kilometers (60 miles) from the border and known as a Hezbollah stronghold, both crosses Nasrallah's "red line" and is a clear shift away from the unofficial rules of engagement.

Recent events have upset "the balance of deterrence," said Amal Saad, a lecturer in politics at Cardiff University in the UK and a longtime observer of Hezbollah.

In order to restore that, Hezbollah will have to respond, she explained. "Whatever happens will have to be swift. They can't allow too much time to lag because Israel has already declared its intention to wage an ongoing campaign of assassinations [of Hamas members]."

Although Israel has suggested these assassinations could happen in Qatar and Turkey too, that seems unlikely, experts agree. Qatar is playing a diplomatic role in hostage negotiations and Israel doesn't want to further upset already tense relations with Turkey. The most likely place for such an act is in Lebanon.

"Hezbollah knows full well that if it doesn't respond to this, firstly that Israel may not only strike another Palestinian target in Lebanon but also that, secondly, it may actually view Hezbollah as weak," she explained. "So they need to carefully calibrate an attack which doesn't embarrass Israel and force it to respond in a more escalatory manner, but which also sends the message that you can't continue with this, you can't use Beirut as a military theater."

"Never, since October 8, has Hezbollah found itself in a position so delicate," Anthony Samrani, editor-in-chief of leading Lebanese newspaper, L'Orient-Le Jour, confirmed in an op-ed this week. "If Hezbollah does nothing, it opens the way for more attacks of this kind in its stronghold. But if the response is too strong, it opens the way to all-out war."

Responding to provocation?

So far, observers have said, Hezbollah does not seem to want to expand its military operations or to respond too firmly to any provocation. As Samrani points out, Hezbollah has not reacted radically to other similar assassinations.

In fact, it is Israel that may be more of "a black box," Saad said. It is hard to say what Israel's intentions are because the country is being run by the most-far-right government it has ever had, and also because Israeli political opinion is divided.

There are also other unanswered questions about this week's assassination in Beirut. The US has been asking its Israeli allies to take a more targeted approach and to avoid killing civilians. Despite a death toll of over 22,000 in Gaza at last count, Israel has been unable to kill many senior Hamas figures inside Gaza. As the Israeli public starts to question its own death toll, observers suggest Israel may now be turning to more easily achievable operations such as Arouri's assassination. In his speech, Hezbollah's Nasrallah suggested the Arouri killing would allow Israeli politicians to claim a victory of sorts. 

This may indicate a new phase of the conflict that is lower intensity, Saad explained.

After all, the incident in Beirut follows on from the December 25 assassination of Seyed Razi Mousavi, a senior Iranian general in Damascus, Syria, by Israel. The US military has clashed directly with Yemen's Houthis, who are holding international shipping to ransom, as well as struck Iran-affiliated militias in Iraq.

On Thursday, a US missile strike killed the commander of one of the latter, Harakat al-Nujaba, in Baghdad. When asked whether Israel was involved in Thursday's assassination, an Israeli spokesperson did not comment, news agencies reported.