Two days of Israeli airstrikes against Palestinian Islamic Jihad militants have killed 24 people in Gaza, in some of the heaviest fighting for months that resulted in widespread bombardment and more than 350 rockets launched from the strip into Israel.

The dead included a 7-year old boy and two other minors, according the Palestinian ministry of health. More than 70 others were wounded, including 30 children and 13 women. In Israel, advanced air defence equipment took out most of the rockets heading for built up areas. However, three people were hit by shrapnel or debris.

Following a brief overnight lull, the violence restarted on Wednesday morning as Islamic Jihad launched further salvos and Israel vowed to retaliate with a round of attacks. The exchange began after Israel carried out two assassination attempts on Tuesday.

“Our jihad is ongoing and our operations are continuing,” Islamic Jihad’s military wing said in a statement, promising to avenge their senior commander, Baha Abu al-Ata, who was killed with his wife on Tuesday while they were sleeping at home.

At least 11 of the fatalities were Islamic Jihad fighters, and three more belonged to a smaller militant faction.

Q&A What is Palestinian Islamic Jihad? Show Hide Islamic Jihad is the second-largest Palestinian militant faction in Gaza after the strip’s rulers, Hamas.

Set up in the late 1970s and early 80s by hardline Islamists, the group has roots in Palestinian refugee camps and is believed to comprise a few thousand fighters. Considered an Iranian proxy force, its leadership is based in the Syrian capital, Damascus. Israel says the group receives millions of dollars in Iranian funding each year. Both Hamas and Islamic Jihad call for Israel’s destruction, attack civilians and are widely designated as terrorist groups. Between the two, Islamic Jihad is deemed more aggressive and reckless, especially as it can focus on military activities rather than governing 2 million people in the Mediterranean enclave. While Hamas and Islamic Jihad maintain a cautious alliance, the latter is believed to have become frustrated with the unofficial truces between Hamas and Israel. Oliver Holmes

In Israel, the prime minister, Benjamin Netanyahu, warned the Iran-backed militants his government would continue to strike with “no mercy”.

“Either stop these attacks or absorb more and more blows,” he said. Naftali Bennett, the new hardline nationalist defence minister, also threatened action. “Anyone who plans to attack us in the day will never be sure to make it through the night. You were and will remain in the crosshairs.”

Sirens blared in multiple Israeli cities, and several people were wounded by rocket debris. In Gaza, schools and government offices were closed, with blasts from strikes ringing out.

The UK-based health charity, Medical Aid for Palestinians (MAP), which works in Gaza, said the attacks come as the enclave faces a chronic shortage of medical supplies, with close to half of all essential drugs including pain killers at dangerously low levels.

“The situation in Gaza has significantly deteriorated again this morning Explosions can be heard all over Gaza. Once again, we are experiencing a situation very similar to the 2014 Gaza attacks,” saod Fikr Shalltoot, MAP’s Director of Programmes in Gaza, recalling the last full-blown war.

The recent clashes ended months of relative quiet, fostered by a truce brokered by Egypt between Israel and Hamas, Gaza’s rulers. Islamic Jihad, a more hardline group in Gaza that is focused almost exclusively on military goals, was not party to the ceasefire.

Hamas and Israel have fought three wars and Israel normally blames, and bombs, the group for any attacks originating out of Gaza. But the ceasefire seemed to have worked for both sides, and they appeared to be promoting the status quo.

While Hamas said it would support its militant allies, it was not clear how many, if any, rockets the group was firing, and Israel focused its strikes on Islamic Jihad.

Israel, which has moved away from the tactic of targeted killings that was long seen as counterproductive, was also accused of attempting to assassinate another senior Islamic Jihad figure on Tuesday. The second attack was in Damascus, Syria, but was not claimed by Israel. Akram al-Ajouri survived when his apartment was hit with a missile, but his son and granddaughter were killed, Syrian state media said.

The strikes and ensuing battles threatened to escalate a conflict between Israel and Iran, which has proxies such as Islamic Jihad across the region. They come at a time in which Israel is also in political paralysis, with two inconclusive elections this year and a potential third on the horizon.