Killing of Bahaa Abu al-Ata in Gaza comes as Palestinian group says its political leader was also targeted in Damascus.
A ceasefire between Islamic Jihad and Israel has largely held in the Gaza Strip since Thursday morning, amid reports of cross-border fire exchange.
The agreement reportedly brokered by Egypt came into effect after two days of cross-border fighting and Israeli air attacks killed at least 34 Palestinians, including eight members of the same family.
Gaza Health Ministry on Thursday identified them as members of the Abu Malhous family from Deir al-Balah area.
At least 63 Israelis received treatment for injuries from rocket attacks launched from Gaza.
Al Jazeera’s Harry Fawcett, reporting from near the Gaza fence, said there seems to be a “real fragility” to the ceasefire, which came into force at 5:30am local time (03:30 GMT), according to the Islamic Jihad group spokesman Musab al-Braim.
“We heard from our colleagues in Gaza, that more rockets have been fired out of Gaza, and around the same time, we heard here what sounded like outgoing Israeli artillery,” Fawcett said, without being able to confirm.
“The ceasefire that had been holding for about four or five hours appears to be less firm,” he noted. “This is what the UN envoy to the region … was warning of. He said the coming hours and days would be crucial in trying to avert a wider war.”
The latest violence escalated after Israel killed top Islamic Jihad commander Bahaa Abu al-Ata in an air raid on Tuesday, deeming him an imminent threat.
Fawcett said that the terms of the ceasefire agreement are a “little bit different, depending on who you listen to”.
Al-Braim told Al Jazeera that his group had secured concessions from Israel.
“The deal included the occupation’s submission to conditions, which is to stop the assassinations, particularly of the protesters in the March of Return demonstrations, and to begin practically the procedures to break the siege,” he said.
According to an Islamic Jihad official, the agreement stipulates that Palestinian factions must ensure a return to calm in Gaza and “maintain peace” during demonstrations, while Israel must stop hostilities and “ensure a ceasefire” during demonstrations by Palestinians.
A top Egyptian official told the AFP news agency that his country had undertaken efforts to end the two days of fighting that saw Israel bombing dozens of houses and farms in the besieged Palestinian enclave.
‘Situation remains tense‘
Israeli military spokesman Avichay Adraee said in a Twitter post that the two-day round of fighting in Gaza “is over”, confirming the ceasefire.
Despite the ceasefire announcement, Israeli Foreign Minister Israel Katz said Israel would follow suit only if Palestinian factions in Gaza stop attacks – denying that Israel had changed open-fire policy as demanded by the Islamic Jihad group for the truce.
“Quiet will be answered with quiet,” Katz said on Thursday in remarks made to local media.
“The State of Israel will not hesitate to strike at those who try to harm it, from the Gaza Strip or from anywhere else.”
Al Jazeera’s Fawcett said that while Islamic Jihad said it had secured from Israel an undertaking not to carry on with targeted assassinations and not to use live fire at the border protests on Fridays, an Israeli official has been quoted in local media as saying that is not the case with regards to the protests.
“Israel doesn’t usually acknowledge ceasefires with groups such as Hamas and the Islamic Jihad … However, it does show that the situation remains tense,” he added.
The Gaza Strip has been under a joint Israeli-Egyptian blockade for more than a decade, which has severely curtailed freedom of movement for the population of two million. The flow of goods and services, as well as medical supplies, is also severely hampered due to the crippling siege.
Palestinians have been gathering near the perimeter fence to participate in the Great March of Return, a series of weekly protests that began in March 2018, calling for an end to the 12-year-old land and air siege.
Since the Gaza rallies began, 313 Palestinian protesters have been killed by Israeli fire and thousands more wounded, according to the health ministry. Eight Israelis have been killed over the same period.
Death of Islamic Jihad commander
Following the Israeli attack that killed Islamic Jihad commander Abu al-Ata in Gaza, the two sides had been exchanging fire, with Israel’s military saying it recorded more than 350 incoming rockets.
Israel said Abu al-Ata was responsible for rocket fire as well as other attacks and was planning more violence, with the military calling him a “ticking bomb”.
In Israel, air raid sirens wailed and fireballs exploded as air defence missiles intercepted rockets, sending Israelis rushing to bomb shelters.
In Gaza, residents surveyed the damage and mourned their dead.
United Nations envoy Nickolay Mladenov arrived in Cairo on Wednesday afternoon, airport officials said, following reports he was to hold talks aimed at halting the fighting.
The UN and Egypt have been instrumental in mediating previous ceasefires between Israel and Gaza-based armed groups.
Israeli Prime Minister Benjamin Netanyahu said on Wednesday that Islamic Jihad must stop its rocket attacks or “absorb more and more blows”.
An Islamic Jihad spokesman had said the group was not interested in mediation as it retaliated over the killing of one of its commanders.
The flare-up raised fears of a new all-out conflict between Israel and Palestinian factions in Gaza, which has seen three major Israeli military operations in the past decade.