The number of Palestinians killed by Israel's offensive in Gaza climbed above 1,000 yesterday, despite repeated calls from the UN for a halt to the conflict.

With mounting concern about the hundreds of civilians killed, nine Israeli human rights groups wrote to their government warning of their "heavy suspicion ... of grave violations of international humanitarian law by military forces".

Among the sites hit yesterday was Sheikh Radwan cemetery. Thirty graves were destroyed, spreading rotting flesh over a wide area. The army said it was targeting a nearby weapons cache.

So far 1,010 Palestinians have died, including 315 children and 95 women, Dr Moawiya Hassanein, head of Gaza's medical emergency services, told the Guardian. The number of injured after 19 days of fighting stood at 4,700, he said. On the Israeli side, 13 people have died, among them three civilians, and four soldiers accidentally killed by their own troops.

The Palestinian Centre for Human Rights, which is based in Gaza and has field staff across the territory, believed at least 673 civilians had been killed - about two-thirds of the total. A more accurate count of civilian deaths is difficult, with journalists and international human rights observers banned from entering Gaza.

Ban Ki-moon, the UN secretary-general, was in Cairo for talks to halt the fighting. "My call is for an immediate end to violence in Gaza, and then to the Israeli military offensive and a halt to rocket attacks by Hamas," he said. "It is intolerable that civilians bear the brunt of this conflict."

Yesterday John Holmes, the UN's humanitarian chief, told the security council: "The situation for the civilian population of Gaza is terrifying, and its psychological impact felt particularly by children and their parents, who feel helpless and unable to protect them."

He added that Hamas's rocket attacks on Israel violated international laws and must cease. "Yet any Israeli response must itself comply with international humanitarian law. Here, too, there is considerable and grave cause for concern."

The Israeli military pressed on with its offensive yesterday, striking 20 sites across Gaza, including what it said were rocket launching sites, three smuggling tunnels, several armed gunmen and five buildings storing weapons.

Yet despite the intense bombing and artillery, militant rocket fire from Gaza has continued every day since the war began. Yesterday at least 16 rockets were fired into southern Israel, some reaching as far as Be'er Sheva and Ashdod.

Separately, guerrillas in southern Lebanon fired rockets into northern Israel yesterday. There were no casualties. The Israeli military fired mortars back.

The nine Israeli human rights groups, which include B'Tselem, Gisha, Amnesty International's Israel section and Physicians for Human Rights, said accounts from Gaza showed the Israeli military was "making wanton use of lethal force" and called for a halt to attacks on civilians, access for civilians to escape the fighting, medical care for the injured, access for medical and rescue teams and the proper operation of electricity, water and sewage systems. Their unusually strong criticisms stand out in a country whose Jewish population at least has been united in extraordinarily strong support for the war in Gaza.

The desperate state of health facilities in Gaza was highlighted yesterday in the Lancet medical journal. Several mobile clinics and ambulances have been damaged by Israeli attacks, it notes, and at least six medical personnel killed. Hospitals and clinics have been forced to close. International law requires that all medical staff and facilities be protected at all times, even during armed conflict, said the Lancet. "Attacks on staff and facilities are serious violations of these laws," it said.

Many doctors are working 24-hour shifts, ambulances cannot be maintained and are breaking down, while hospital equipment, medicines and anaesthetics, beds and medical staff are all in short supply. Hospitals and clinics have had their electricity supplies cut and are relying on "fragile back-up generators".

Norwegian doctors Mads Gilbert and Erik Fosse wrote that during their spell working in al-Shifa hospital in Gaza City in the current conflict they had "witnessed the most horrific war injuries in men, women and children of all ages in numbers almost too large to comprehend. The wounded, dying and dead have streamed into the overcrowded hospital in endless convoys of ambulances and private cars and wrapped in blankets in the caring arms of others. The endless and intense bombardments from Israeli air, ground and naval forces have missed no targets, not even the hospital."

Two Palestinian journalists working for an Iranian television station were charged in Israel yesterday with passing classified information to the enemy. They were accused of reporting the start of the ground invasion two weeks ago while the information was still under military censorship, and could face lengthy jail terms.