Israel has said it was forced to launch a "pre-emptive" operation against Islamic Jihad, insisting the group was planning an imminent attack following days of tensions along the Gaza border.

Health authorities in Gaza, a Palestinian enclave controlled by the Islamist group Hamas, said 10 people have been killed by Israel's bombardment, including a five-year-old girl, with 79 others injured. Israel's army estimated that its operation has killed 15 militants.

Early on Saturday Israel broadened its operation against Islamic Jihad, a group that is aligned with Hamas but often acts independently.

The Israeli army announced the arrest of 19 people it said were members of the group in the occupied West Bank, alongside the arrest of one other person.

Israel and Islamic Jihad have both confirmed the killing of Taysir al-Jabari, a key leader of the militants, in a Friday strike on a building in the west of Gaza city.

Islamic Jihad said that initial Israeli bombardment amounted to a "declaration of war", before it unleashed a barrage of rockets towards Israel.

The rocket fire and Israeli strikes were continuing early Saturday, risking a repeat of an 11-day conflict in May 2021 that devastated Gaza and forced countless Israelis to rush to bomb shelters.

- Escalation, mediation -

"Israel isn't interested in a wider conflict in Gaza, but will not shy away from one either," Prime Minister Yair Lapid said in a nationally televised address on Friday.

Air raid sirens sounded across southern Israel early Saturday, but there were no immediate reports of casualties or major damage, with many rockets intercepted by the Iron Dome aerial defence system.

Officials in border areas urged people to stay close to shelters, which have also been opened in the commercial capital of Tel Aviv.

Egypt, a historic broker between Israel and armed groups in Gaza, was seeking to mediate and may host an Islamic Jihad delegation later Saturday, Egyptian officials told AFP in Gaza.

Hamas has fought four wars with Israel since seizing control of Gaza in 2007, including the conflict last May.

Both Hamas and Islamic Jihad are considered terrorist organisations by much of the West.

A flare up with Islamic Jihad came in 2019, following Israel's killing of Baha Abu al-Ata, Jabari's predecessor.

The sides exchanged fire for several days without Hamas joining the fray.

Hamas's moves amid the current violence could prove crucial in determining its severity, with the group facing pressure from some to maintain calm in order to improve economic conditions in the territory.

Gaza City resident Abdullah al-Arayshi said the situation was "very tense".

"The country is ravaged. We've had enough of wars. Our generation has lost its future," he told AFP.

Streets were largely deserted in Gaza City early Saturday, with many shops shuttered, and daily life largely paralysed, an AFP reporter said.

- Five-year-old girl -

Fire balls and plumes of smoke have billowed out of targets hit in Gaza, but there were no reports of new casualties in recent hours.

On Friday, the health ministry reported "a five-year-old girl, targeted by the Israeli occupation" was among those killed.

Five-year-old Alaa Kaddum had a pink bow in her hair and a wound on her forehead, as her body was carried by her father at her funeral.

Hundreds of mourners gathered in Gaza City for the funerals of Jabari and others killed in the air strikes.

Israeli military spokesman Richard Hecht said "we are assuming about 15 killed in action" in Gaza, referring to Palestinian combatants.

Israeli tanks were lined up along the border and the military said Thursday it was reinforcing its troops.

The strikes come four days after Israel closed its two border crossings with Gaza and restricted the movement of Israeli civilians living near the frontier, citing security concerns.

The measures followed the arrest in the occupied West Bank of two senior members of Islamic Jihad, including Bassem al-Saadi, who Israel accuses of orchestrating recent attacks.

Israel has conducted a near relentless wave of raids inside the West Bank since mid-March in response to deadly attacks on Israeli citizens.

Islamic Jihad did not launch rockets after Saadi's arrest, but Israel has insisted through the week that the group was committed to seeking revenge.