Fears of an all-out conflict in the Middle East have grown as Iran and Hezbollah are mulling a response to suspected and confirmed Israeli attacks that killed senior officials of both Hamas and Hezbollah.

Hezbollah's leader Sayyed Hassan Nasrallah on Tuesday vowed to retaliate for an Israeli strike last week that killed Fuad Shukr, the group's military commander, and said he will defy international calls against it.

"Nobody in Lebanon or abroad can ask us to deal with the aggression that happened last Tuesday as a normal aggression within the context of the battle that has been going on for 10 months," he told a crowd in Beirut's southern suburbs.

Hezbollah fighters have been exchanging fire with Israeli forces in what Nasrallah called regular fighting in parallel with Israel's war in Gaza, which stretched into its 11th month on Wednesday. This time, the group's response would be more powerful, he said.

The Israeli strike on Beirut, which sources told Reuters shattered diplomatic understandings, is believed to be a response to a rocket attack on the Israeli-annexed Golan Heights that killed 12 children. Israel attributed that attack to Hezbollah, which denies involvement.

Nasrallah's remarks also came a day after Iran's Ministry of Foreign Affairs said Israel must be "punished" for killing Hamas political leader Ismail Haniyeh in Tehran on July 31, a charge Israel has neither confirmed nor denied.

Both Hezbollah and Tehran did not specify when and how they will respond. 

The United States, Israel's closest ally, has been attempting to prevent the conflict from escalating through diplomatic channels, though Iran and its allies blamed regional instability on the U.S.'s support for Israel's war in Gaza.

Israel has launched a relentless assault on the Palestinian enclave since Hamas fighters stormed southern Israel in a surprise attack on October 7, killing 1,200 Israelis and foreigners and seizing some 250 hostages, according to Israeli tallies.

Much of Gaza has been reduced to rubble, while a humanitarian disaster has devastated the 2.3 million Palestinians living in the coastal enclave. Palestinian health officials say more than 39,000 Palestinians have been killed by Israeli forces.

Despite a ground invasion that has stretched across Gaza, Hamas appears to still have the capacity to engage in gun battles with Israeli troops and launch rockets into Israel. The Israel Defense Forces claims it has killed or incapacitated some 14,000 Hamas fighters.

The war, which has drawn widespread international condemnation, was halted only once for a brief period after a truce deal was reached in November. All ceasefire talks have faltered since then, with Israel and Hamas blaming each other for adding unacceptable conditions.

Hostilities between Israel and Hamas have also spread to other parts of the Middle East, where the U.S. has increased its military presence and traded attacks with Iran-aligned groups.

In the meantime, the U.S. has failed repeatedly to rein in Israel on some of its key decisions in Gaza and in the broader region, though Secretary of State Antony Blinken said on Tuesday that talks to achieve a ceasefire deal, which Washington deems necessary to cool down regional tensions, had reached their final stage and should end very soon.

That optimism may be put in doubt as Hamas on Tuesday named its Gaza leader Yahya Sinwar, who the Israelis believe was the mastermind behind Hamas's October 7 attack, as the successor to Haniyeh. U.S. President Joe Biden said last week that the killing of Haniyeh itself was not helpful for reaching a ceasefire deal.

Whether or not a ceasefire deal is reached, analysts say both Israel and Iran are likely to exercise restraint as they have since October 7 in order not to be thrust into an all-out regional war. 

On April 13, Iran launched its first-ever strike on Israeli territory in retaliation for an attack on its diplomatic compound in Syria. The Iranian salvo caused no fatalities, and Tehran claimed it had given neighboring countries and the U.S. 72 hours' notice that it would launch the strike, a move that would have allowed them to make preparatory arrangements. Israel is believed to have responded in a restrained counterattack near the Iranian city of Isfahan.

The most important principle for the two countries is not to escalate tensions into a total war, Dong Manyuan, a senior research fellow specialized in Middle East studies and ethnic issues from the China Institute of International Studies, told China Media Group.

"With that principle in mind, Iran and its allies in the Axis of Resistance will need time to prepare for a retaliation," he said, adding that they will need to exchange intelligence, get a clear understanding of Israel's military situation and decide which target they should hit.

For Israel, which has to focus on its war against Hamas, it also does not want to go to war with Iran, Dong said.