He was speaking as he left Germany’s capital Berlin, where he had met German, French and British leaders.
Airstrikes on Friday hit the homes of three families in the camp, wounding more than 85 people, some seriously, according to a statement from Gaza’s Hamas-run government press office.
He added that the final death toll could reach 50 as people were buried under the rubble of the building.
The report cannot be independently verified. According to local sources, northern Gaza is virtually isolated and communication and internet services in the area are cut off.
A video circulated on social media, which the BBC has not confirmed, appears to show a body wrapped in a white shroud lying in the courtyard of Al Awda Hospital.
The hospital director told reporters that casualties were rising significantly.
“Ambulance crews are still attempting to rescue the martyrs and the wounded in Jabalia,” the chief said.
“Our hospital wards are full and many injured people are being treated on the floor.”
According to Reuters, the Hamas-run Gaza health ministry said at least 39 Palestinians were killed in Israeli airstrikes on the Friday before the attack, many of them in Jabalia.
About 400,000 people were trapped in the camp without food or water for more than two weeks.
Georgios Petropoulos, head of the UN Humanitarian Aid Office, told the BBC’s NewsHour program that Jabalia’s family was enduring “horrible conditions”.
“We cannot sound the alarm enough about how dire and dangerous the situation for civilians is,” he said in Rafah, southern Gaza.
Israel said on Friday it had sent about 30 shipments of supplies, including food, water, medical supplies and shelter equipment, to the northern Gaza Strip, but local health officials told Reuters the relief supplies had not reached the worst-hit areas, including Jabalia.
Israel has repeatedly denied that it is preventing humanitarian aid from entering the Gaza Strip, but the United States has said some U.S. military aid risks being cut off unless access is increased.
Israeli Minister Amichai Chikli told the BBC that Israel had placed a “blockade” on areas in northern Gaza, including Jabalia.
“We allowed civilians to escape to safe areas and prevented supplies from entering the blockade area,” he told the NewsHour programme.
He insisted this was “legal under international law.”
