Israel pounded Gaza with air strikes Friday, killing more than 15 people, including a top militant, and triggering a barrage of retaliatory rocket fire from the territory.
Palestinian group Islamic Jihad said the Israeli bombardment amounted to a "declaration of war", hours before it unleashed what it said was an "initial response" of 100 rockets towards Israel.
There were no immediate reports of casualties inside Israel. But in Gaza, a child was among those killed, according to the territory's health ministry, which is run by Hamas.
Call for immediate halt of aggression
The Palestinian Presidency Friday evening called for the immediate halt of Israeli aggression, blaming the Israeli occupation for this dangerous escalation.
In a statement, the presidency called on the international community to compel the Israeli occupation to stop its aggression against the Palestinian people everywhere, specifically in Gaza, and to provide them with international protection.
The Israeli strikes were ongoing late Friday, targeting what the army described as militant targets across the territory it has blockaded since the Hamas takeover.
Flames poured out of a building in Gaza City following the first round of strikes, while wounded Palestinians were evacuated by medics.
Gaza's health ministry reported "a five-year-old girl, targeted by the Israeli occupation" was among those killed. A further 55 Palestinians were wounded, the ministry said. 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.
Islamic Jihad said several members of its military wing were among those killed, including "the great fighter Taysir al-Jabari 'Abu Mahmoud', the commander of the Al-Quds Brigade in the northern region of the Gaza Strip."
Hundreds of mourners gathered in Gaza City for the funerals of Jabari and others killed in the air strikes.
Israeli tanks were lined up along the border and the military said on 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 follow the arrest in the occupied West Bank of two senior members of Islamic Jihad, which has a strong presence in Gaza.
The group did not launch attacks on Israeli territory after the arrests.
Hamas said Israel has "committed a new crime for which it must pay the price".
"The resistance in all its military arms and factions is united in this struggle and will speak loudly...All fronts must open fire on the enemy," Hamas said in a statement.
Palestinians including patients and those with Israeli work permits have been prevented from leaving the Gaza Strip since Tuesday, while the goods crossing has also been shut.
Gaza's only power station is at risk of imminent outage due to a lack of fuel supplies through Israel, its manager warned on Thursday.
This week's shutdown of the border area follows a raid by security forces in the northern West Bank district of Jenin.
Israeli forces detained Bassem al-Saadi and another senior member of Islamic Jihad.
A 17-year-old member of the group was shot dead by Israeli forces during the raid.