Iran's supreme leader vowed retaliation on Saturday for attacks by Israel, while an unspecified strike on a polio vaccination facility in Gaza wounded six, including children.
Days before the presidential election in the United States — Israel's main military supplier — Ayatollah Ali Khamenei said Iran's response would cover attacks on both the Islamic republic and its allies.
"The enemies, both the US and the Zionist regime (Israel), should know that they will definitely receive a tooth-breaking response," Khamenei said, referring to Iran-aligned groups including those in Yemen and Syria.
On Oct 26, Israel bombed military sites in Iran, killing four servicemen, in response to an Oct 1 barrage of about 200 missiles that Teheran called a reprisal.
Israel has warned Iran against responding to the Oct 26 attack.
Analysts say Israel inflicted severe damage on Iranian air defenses and missile capacities and could yet launch more wide-scale action against Iran.
Meanwhile, the US military said on Saturday that its B-52 bombers have arrived in the Middle East, a day after Washington announced their deployment in a warning to Teheran.
Since late September, Israel has been engaged in a full-scale conflict with Hezbollah in Lebanon while fighting continues in Gaza against the Palestinian militant group Hamas.
Israeli forces have carried out a major air and ground assault since Oct 6 in northern Gaza, centered on the Jabalia area, vowing to stop Hamas from regrouping.
The World Health Organization said four children were among six people wounded in a strike on a polio vaccination center in northern Gaza, where United Nations agencies have spoken of "apocalyptic "conditions in the face of a blistering Israeli assault.
Worrying report
WHO chief Tedros Adhanom Ghebreyesus said the agency had received "an extremely concerning report" about a strike on the Sheikh Radwan health center.
The facility "was struck today while parents were bringing their children to the lifesaving polio vaccination" drive, he said.
Tedros did not specify who carried out the strike, but a source in Gaza's civil defense agency told AFP that it was "an Israeli quadcopter that fired two missiles which hit the wall of Sheikh Radwan clinic".
The Israeli military denied striking near the clinic at the time.
The UN children's agency said "the attacks on Jabalia, the vaccination clinic and the UNICEF staff member are yet further examples of the grave consequences of the indiscriminate strikes on civilians in the Gaza Strip".
UNICEF chief Catherine Russell said 50 children had been reported killed over 48 hours in Jabalia.
"Taken alongside the horrific level of child deaths in North Gaza from other attacks, these most recent events combine to write yet another dark chapter in one of the darkest periods of this terrible war," she said in a statement on Saturday.
Israel's military said dozens of militants were killed around Jabalia "in aerial and ground activity".
On Sunday, Israeli forces stepped up bombardment of the Gaza Strip, killing at least 23 people, Palestinian medics said.
They said at least 13 Palestinians were killed in separate attacks on houses in Beit Lahiya town and Jabalia. The rest were killed in separate Israeli airstrikes in Gaza City and the southern areas.
In addition, after nearly a year of tit-for-tat exchanges across Israel's northern border, Israel escalated its bombing campaign against Hezbollah targets in Lebanon on Sept 23 and later sent in ground troops.
Hezbollah has since fired more deeply into Israel.
On Friday, Israeli naval commandos seized a trainee mariner whom a military official described as a "senior operative" of Hezbollah in a raid in northern Lebanon and brought him to Israel.
Lebanese caretaker Prime Minister Najib Mikati instructed the Foreign Ministry to submit a complaint to the UN Security Council over the raid in the coastal town of Batroun, his office said.
